diff --git a/Pipfile b/Pipfile
index aca7dc7f..d9795ba9 100644
--- a/Pipfile
+++ b/Pipfile
@@ -24,3 +24,5 @@ mock = "~=3.0"
 pylint = "~=2.4"
 astroid = "~=2.3"
 isort = "~=4.3"
+
+mypy = "==0.761"
diff --git a/README.md b/README.md
index 9cb50efc..50834ce6 100644
--- a/README.md
+++ b/README.md
@@ -45,14 +45,18 @@ download and unarchive the source tarball (Appium-Python-Client-X.X.tar.gz).
 
 - Style Guide: https://www.python.org/dev/peps/pep-0008/
     - `autopep8` helps to format code automatically
-        ```
+        ```shell
         $ python -m autopep8 -r --global-config .config-pep8 -i .
         ```
     - `isort` helps to order imports automatically
-        ```
+        ```shell
         $ python -m isort -rc .
         ```
         - When you use newly 3rd party modules, add it to [.isort.cfg](.isort.cfg) to keep import order correct
+    - `mypy` helps to check explicit type declarations
+        ```shell
+        $ python -m mypy appium
+        ```
 - Docstring style: Google Style
     - Refer [link](https://sphinxcontrib-napoleon.readthedocs.io/en/latest/example_google.html)
 - You can customise `CHANGELOG.rst` with commit messages following [.gitchangelog.rc](.gitchangelog.rc)
diff --git a/appium/common/helper.py b/appium/common/helper.py
index b694b9fa..d34417fb 100644
--- a/appium/common/helper.py
+++ b/appium/common/helper.py
@@ -12,44 +12,25 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from collections import OrderedDict
+from typing import Dict
 
 from appium import version as appium_version
 
 
-def appium_bytes(value, encoding):
-    """Return a bytes-like object
-
-    Has _appium_ prefix to avoid overriding built-in bytes.
-
-    Args:
-        value (str): A value to convert
-        encoding (str): A encoding which will convert to
-
-    Returns:
-        str: A bytes-like object
-    """
-
-    try:
-        return bytes(value, encoding)  # Python 3
-    except TypeError:
-        return value  # Python 2
-
-
-def extract_const_attributes(cls):
+def extract_const_attributes(cls: type) -> Dict:
     """Return dict with constants attributes and values in the class(e.g. {'VAL1': 1, 'VAL2': 2})
 
     Args:
         cls (type): Class to be extracted constants
 
     Returns:
-        OrderedDict: dict with constants attributes and values in the class
+        dict: dict with constants attributes and values in the class
     """
-    return OrderedDict(
-        [(attr, value) for attr, value in vars(cls).items() if not callable(getattr(cls, attr)) and attr.isupper()])
+    return dict([(attr, value) for attr, value in vars(cls).items()
+                 if not callable(getattr(cls, attr)) and attr.isupper()])
 
 
-def library_version():
+def library_version() -> str:
     """Return a version of this python library
     """
 
diff --git a/appium/common/logger.py b/appium/common/logger.py
index 372d7fa8..014b69e4 100644
--- a/appium/common/logger.py
+++ b/appium/common/logger.py
@@ -16,7 +16,7 @@
 import sys
 
 
-def setup_logger(level=logging.NOTSET):
+def setup_logger(level: int = logging.NOTSET) -> None:
     logger.propagate = False
     logger.setLevel(level)
     handler = logging.StreamHandler(stream=sys.stderr)
diff --git a/appium/saucetestcase.py b/appium/saucetestcase.py
index 8192f504..a2e94aba 100644
--- a/appium/saucetestcase.py
+++ b/appium/saucetestcase.py
@@ -19,6 +19,7 @@
 import os
 import sys
 import unittest
+from typing import Any, Callable, List
 
 from sauceclient import SauceClient
 
@@ -29,8 +30,8 @@
 sauce = SauceClient(SAUCE_USERNAME, SAUCE_ACCESS_KEY)
 
 
-def on_platforms(platforms):
-    def decorator(base_class):
+def on_platforms(platforms: List[str]) -> Callable[[type], None]:
+    def decorator(base_class: type) -> None:
         module = sys.modules[base_class.__module__].__dict__
         for i, platform in enumerate(platforms):
             name = "%s_%s" % (base_class.__name__, i + 1)
@@ -40,16 +41,16 @@ def decorator(base_class):
 
 
 class SauceTestCase(unittest.TestCase):
-    def setUp(self):
-        self.desired_capabilities['name'] = self.id()
+    def setUp(self) -> None:
+        self.desired_capabilities['name'] = self.id()  # type: ignore
         sauce_url = "http://%s:%s@ondemand.saucelabs.com:80/wd/hub"
         self.driver = webdriver.Remote(
-            desired_capabilities=self.desired_capabilities,
+            desired_capabilities=self.desired_capabilities,  # type: ignore
             command_executor=sauce_url % (SAUCE_USERNAME, SAUCE_ACCESS_KEY)
         )
         self.driver.implicitly_wait(30)
 
-    def tearDown(self):
+    def tearDown(self) -> None:
         print("Link to your job: https://saucelabs.com/jobs/%s" % self.driver.session_id)
         try:
             if sys.exc_info() == (None, None, None):
diff --git a/appium/webdriver/appium_connection.py b/appium/webdriver/appium_connection.py
index 719923fd..f89998af 100644
--- a/appium/webdriver/appium_connection.py
+++ b/appium/webdriver/appium_connection.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Any, Dict
+
 from selenium.webdriver.remote.remote_connection import RemoteConnection
 
 from appium.common.helper import library_version
@@ -20,7 +22,7 @@
 class AppiumConnection(RemoteConnection):
 
     @classmethod
-    def get_remote_connection_headers(cls, parsed_url, keep_alive=True):
+    def get_remote_connection_headers(cls, parsed_url: str, keep_alive: bool = True) -> Dict[str, Any]:
         """Override get_remote_connection_headers in RemoteConnection"""
         headers = RemoteConnection.get_remote_connection_headers(parsed_url, keep_alive=keep_alive)
         headers['User-Agent'] = 'appium/python {} ({})'.format(library_version(), headers['User-Agent'])
diff --git a/appium/webdriver/appium_service.py b/appium/webdriver/appium_service.py
index 42527c24..7683782a 100644
--- a/appium/webdriver/appium_service.py
+++ b/appium/webdriver/appium_service.py
@@ -12,11 +12,11 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-
 import os
-import subprocess
+import subprocess as sp
 import sys
 import time
+from typing import Any, List, Optional, TypeVar, Union
 
 import urllib3
 
@@ -27,7 +27,7 @@
 STATUS_URL = '/wd/hub/status'
 
 
-def find_executable(executable):
+def find_executable(executable: str) -> Optional[str]:
     path = os.environ['PATH']
     paths = path.split(os.pathsep)
     base, ext = os.path.splitext(executable)
@@ -45,7 +45,7 @@ def find_executable(executable):
     return None
 
 
-def poll_url(host, port, path, timeout_ms):
+def poll_url(host: str, port: int, path: str, timeout_ms: int) -> bool:
     time_started_sec = time.time()
     while time.time() < time_started_sec + timeout_ms / 1000.0:
         try:
@@ -64,12 +64,15 @@ class AppiumServiceError(RuntimeError):
     pass
 
 
+T = TypeVar('T', bound='AppiumService')
+
+
 class AppiumService(object):
-    def __init__(self):
-        self._process = None
-        self._cmd = None
+    def __init__(self) -> None:
+        self._process: Optional[sp.Popen] = None
+        self._cmd: Optional[List] = None
 
-    def _get_node(self):
+    def _get_node(self) -> str:
         if not hasattr(self, '_node_executable'):
             self._node_executable = find_executable('node')
         if self._node_executable is None:
@@ -77,7 +80,7 @@ def _get_node(self):
                                      'Make sure it is installed and present in PATH')
         return self._node_executable
 
-    def _get_npm(self):
+    def _get_npm(self) -> str:
         if not hasattr(self, '_npm_executable'):
             self._npm_executable = find_executable('npm.cmd' if sys.platform == 'win32' else 'npm')
         if self._npm_executable is None:
@@ -85,41 +88,41 @@ def _get_npm(self):
                                      'Make sure it is installed and present in PATH')
         return self._npm_executable
 
-    def _get_main_script(self):
+    def _get_main_script(self) -> Union[str, bytes]:
         if not hasattr(self, '_main_script'):
             for args in [['root', '-g'], ['root']]:
                 try:
-                    modules_root = subprocess.check_output([self._get_npm()] + args).strip().decode('utf-8')
+                    modules_root = sp.check_output([self._get_npm()] + args).strip().decode('utf-8')
                     if os.path.exists(os.path.join(modules_root, MAIN_SCRIPT_PATH)):
-                        self._main_script = os.path.join(modules_root, MAIN_SCRIPT_PATH)
+                        self._main_script: Union[str, bytes] = os.path.join(modules_root, MAIN_SCRIPT_PATH)
                         break
-                except subprocess.CalledProcessError:
+                except sp.CalledProcessError:
                     continue
             if not hasattr(self, '_main_script'):
                 try:
-                    self._main_script = subprocess.check_output(
+                    self._main_script = sp.check_output(
                         [self._get_node(),
                          '-e',
                          'console.log(require.resolve("{}"))'.format(MAIN_SCRIPT_PATH)]).strip()
-                except subprocess.CalledProcessError as e:
+                except sp.CalledProcessError as e:
                     raise AppiumServiceError(e.output)
         return self._main_script
 
     @staticmethod
-    def _parse_port(args):
+    def _parse_port(args: List[str]) -> int:
         for idx, arg in enumerate(args or []):
             if arg in ('--port', '-p') and idx < len(args) - 1:
                 return int(args[idx + 1])
         return DEFAULT_PORT
 
     @staticmethod
-    def _parse_host(args):
+    def _parse_host(args: List[str]) -> str:
         for idx, arg in enumerate(args or []):
             if arg in ('--address', '-a') and idx < len(args) - 1:
                 return args[idx + 1]
         return DEFAULT_HOST
 
-    def start(self, **kwargs):
+    def start(self, **kwargs: Any) -> sp.Popen:
         """Starts Appium service with given arguments.
 
         The service will be forcefully restarted if it is already running.
@@ -153,31 +156,31 @@ def start(self, **kwargs):
 
         env = kwargs['env'] if 'env' in kwargs else None
         node = kwargs['node'] if 'node' in kwargs else self._get_node()
-        stdout = kwargs['stdout'] if 'stdout' in kwargs else subprocess.PIPE
-        stderr = kwargs['stderr'] if 'stderr' in kwargs else subprocess.PIPE
+        stdout = kwargs['stdout'] if 'stdout' in kwargs else sp.PIPE
+        stderr = kwargs['stderr'] if 'stderr' in kwargs else sp.PIPE
         timeout_ms = int(kwargs['timeout_ms']) if 'timeout_ms' in kwargs else STARTUP_TIMEOUT_MS
         main_script = kwargs['main_script'] if 'main_script' in kwargs else self._get_main_script()
         args = [node, main_script]
         if 'args' in kwargs:
             args.extend(kwargs['args'])
         self._cmd = args
-        self._process = subprocess.Popen(args=args, stdout=stdout, stderr=stderr, env=env)
+        self._process = sp.Popen(args=args, stdout=stdout, stderr=stderr, env=env)
         host = self._parse_host(args)
         port = self._parse_port(args)
-        error_msg = None
+        error_msg: Optional[str] = None
         if not self.is_running or (timeout_ms > 0 and not poll_url(host, port, STATUS_URL, timeout_ms)):
             error_msg = 'Appium has failed to start on {}:{} within {}ms timeout'\
                         .format(host, port, timeout_ms)
         if error_msg is not None:
-            if stderr == subprocess.PIPE:
+            if stderr == sp.PIPE:
                 err_output = self._process.stderr.read()
                 if err_output:
-                    error_msg += '\nOriginal error: {}'.format(err_output)
+                    error_msg += '\nOriginal error: {}'.format(str(err_output))
             self.stop()
             raise AppiumServiceError(error_msg)
         return self._process
 
-    def stop(self):
+    def stop(self) -> bool:
         """Stops Appium service if it is running.
 
         The call will be ignored if the service is not running
@@ -188,14 +191,14 @@ def stop(self):
         """
         is_terminated = False
         if self.is_running:
-            self._process.terminate()
+            self._process.terminate()  # type: ignore
             is_terminated = True
         self._process = None
         self._cmd = None
         return is_terminated
 
     @property
-    def is_running(self):
+    def is_running(self) -> bool:
         """Check if the service is running.
 
         Returns:
@@ -204,7 +207,7 @@ def is_running(self):
         return self._process is not None and self._process.poll() is None
 
     @property
-    def is_listening(self):
+    def is_listening(self) -> bool:
         """Check if the service is listening on the given/default host/port.
 
         The fact, that the service is running, does not always mean it is listening.
diff --git a/appium/webdriver/common/multi_action.py b/appium/webdriver/common/multi_action.py
index f80a111f..f3326534 100644
--- a/appium/webdriver/common/multi_action.py
+++ b/appium/webdriver/common/multi_action.py
@@ -19,17 +19,25 @@
 # chaining as the spec requires.
 
 import copy
+from typing import TYPE_CHECKING, Dict, List, Optional, TypeVar, Union
 
 from appium.webdriver.mobilecommand import MobileCommand as Command
 
+if TYPE_CHECKING:
+    from appium.webdriver.webdriver import WebDriver
+    from appium.webdriver.webelement import WebElement
+    from appium.webdriver.common.touch_action import TouchAction
+
+T = TypeVar('T', bound='MultiAction')
+
 
 class MultiAction(object):
-    def __init__(self, driver, element=None):
+    def __init__(self, driver: 'WebDriver', element: Optional['WebElement'] = None) -> None:
         self._driver = driver
         self._element = element
-        self._touch_actions = []
+        self._touch_actions: List['TouchAction'] = []
 
-    def add(self, *touch_actions):
+    def add(self, *touch_actions: 'TouchAction') -> None:
         """Add TouchAction objects to the MultiAction, to be performed later.
 
         Args:
@@ -49,7 +57,7 @@ def add(self, *touch_actions):
 
             self._touch_actions.append(copy.copy(touch_action))
 
-    def perform(self):
+    def perform(self: T) -> T:
         """Perform the actions stored in the object.
 
         Usage:
@@ -68,7 +76,7 @@ def perform(self):
         return self
 
     @property
-    def json_wire_gestures(self):
+    def json_wire_gestures(self) -> Dict[str, Union[List, str]]:
         actions = []
         for action in self._touch_actions:
             actions.append(action.json_wire_gestures)
diff --git a/appium/webdriver/common/touch_action.py b/appium/webdriver/common/touch_action.py
index 84668e17..a8fb299d 100644
--- a/appium/webdriver/common/touch_action.py
+++ b/appium/webdriver/common/touch_action.py
@@ -24,16 +24,25 @@
 # pylint: disable=no-self-use
 
 import copy
+from typing import TYPE_CHECKING, Dict, List, Optional, TypeVar, Union
 
 from appium.webdriver.mobilecommand import MobileCommand as Command
 
+if TYPE_CHECKING:
+    from appium.webdriver.webelement import WebElement
+    from appium.webdriver.webdriver import WebDriver
+
+T = TypeVar('T', bound='TouchAction')
+
 
 class TouchAction(object):
-    def __init__(self, driver=None):
+
+    def __init__(self, driver: Optional['WebDriver'] = None):
         self._driver = driver
-        self._actions = []
+        self._actions: List = []
 
-    def tap(self, element=None, x=None, y=None, count=1):
+    def tap(self: T, element: Optional['WebElement'] = None, x: Optional[int]
+            = None, y: Optional[int] = None, count: int = 1) -> T:
         """Perform a tap action on the element
 
         Args:
@@ -50,7 +59,8 @@ def tap(self, element=None, x=None, y=None, count=1):
 
         return self
 
-    def press(self, el=None, x=None, y=None, pressure=None):
+    def press(self: T, el: Optional['WebElement'] = None, x: Optional[int] = None,
+              y: Optional[int] = None, pressure: Optional[float] = None) -> T:
         """Begin a chain with a press down action at a particular element or point
 
         Args:
@@ -67,7 +77,8 @@ def press(self, el=None, x=None, y=None, pressure=None):
 
         return self
 
-    def long_press(self, el=None, x=None, y=None, duration=1000):
+    def long_press(self: T, el: Optional['WebElement'] = None, x: Optional[int]
+                   = None, y: Optional[int] = None, duration: int = 1000) -> T:
         """Begin a chain with a press down that lasts `duration` milliseconds
 
         Args:
@@ -83,7 +94,7 @@ def long_press(self, el=None, x=None, y=None, duration=1000):
 
         return self
 
-    def wait(self, ms=0):
+    def wait(self: T, ms: int = 0) -> T:
         """Pause for `ms` milliseconds.
 
         Args:
@@ -101,7 +112,7 @@ def wait(self, ms=0):
 
         return self
 
-    def move_to(self, el=None, x=None, y=None):
+    def move_to(self: T, el: Optional['WebElement'] = None, x: Optional[int] = None, y: Optional[int] = None) -> T:
         """Move the pointer from the previous point to the element or point specified
 
         Args:
@@ -116,7 +127,7 @@ def move_to(self, el=None, x=None, y=None):
 
         return self
 
-    def release(self):
+    def release(self: T) -> T:
         """End the action by lifting the pointer off the screen
 
         Returns:
@@ -126,12 +137,14 @@ def release(self):
 
         return self
 
-    def perform(self):
+    def perform(self: T) -> T:
         """Perform the action by sending the commands to the server to be operated upon
 
         Returns:
             `TouchAction`: self instance
         """
+        if self._driver is None:
+            raise TypeError('Set driver to constructor as a argument when to create the instance.')
         params = {'actions': self._actions}
         self._driver.execute(Command.TOUCH_ACTION, params)
 
@@ -141,23 +154,24 @@ def perform(self):
         return self
 
     @property
-    def json_wire_gestures(self):
+    def json_wire_gestures(self) -> List[Dict]:
         gestures = []
         for action in self._actions:
             gestures.append(copy.deepcopy(action))
         return gestures
 
-    def _add_action(self, action, options):
+    def _add_action(self, action: str, options: Dict) -> None:
         gesture = {
             'action': action,
             'options': options,
         }
         self._actions.append(gesture)
 
-    def _get_opts(self, element, x, y, duration=None, pressure=None):
+    def _get_opts(self, el: Optional['WebElement'] = None, x: Optional[int] = None, y: Optional[int] = None,
+                  duration: Optional[int] = None, pressure: Optional[float] = None) -> Dict[str, Union[int, float]]:
         opts = {}
-        if element is not None:
-            opts['element'] = element.id
+        if el is not None:
+            opts['element'] = el.id
 
         # it makes no sense to have x but no y, or vice versa.
         if x is not None and y is not None:
diff --git a/appium/webdriver/errorhandler.py b/appium/webdriver/errorhandler.py
index 1fa793ba..38426992 100644
--- a/appium/webdriver/errorhandler.py
+++ b/appium/webdriver/errorhandler.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Dict
+
 from selenium.common.exceptions import WebDriverException
 from selenium.webdriver.remote import errorhandler
 
@@ -19,7 +21,7 @@
 
 
 class MobileErrorHandler(errorhandler.ErrorHandler):
-    def check_response(self, response):
+    def check_response(self, response: Dict) -> None:
         try:
             super(MobileErrorHandler, self).check_response(response)
         except WebDriverException as wde:
diff --git a/appium/webdriver/extensions/action_helpers.py b/appium/webdriver/extensions/action_helpers.py
index 108fcfd5..98ddbf67 100644
--- a/appium/webdriver/extensions/action_helpers.py
+++ b/appium/webdriver/extensions/action_helpers.py
@@ -12,15 +12,20 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import List, Optional, Tuple, TypeVar
+
 from selenium import webdriver
 
 from appium.webdriver.common.multi_action import MultiAction
 from appium.webdriver.common.touch_action import TouchAction
+from appium.webdriver.webelement import WebElement
+
+T = TypeVar('T', bound='ActionHelpers')
 
 
 class ActionHelpers(webdriver.Remote):
 
-    def scroll(self, origin_el, destination_el, duration=None):
+    def scroll(self, origin_el: WebElement, destination_el: WebElement, duration: Optional[int] = None) -> T:
         """Scrolls from one element to another
 
         Args:
@@ -47,7 +52,7 @@ def scroll(self, origin_el, destination_el, duration=None):
             action.press(origin_el).wait(duration).move_to(destination_el).release().perform()
         return self
 
-    def drag_and_drop(self, origin_el, destination_el):
+    def drag_and_drop(self, origin_el: WebElement, destination_el: WebElement) -> T:
         """Drag the origin element to the destination element
 
         Args:
@@ -61,7 +66,7 @@ def drag_and_drop(self, origin_el, destination_el):
         action.long_press(origin_el).move_to(destination_el).release().perform()
         return self
 
-    def tap(self, positions, duration=None):
+    def tap(self, positions: List[Tuple], duration: Optional[int] = None) -> T:
         """Taps on an particular place with up to five fingers, holding for a
         certain time
 
@@ -100,7 +105,7 @@ def tap(self, positions, duration=None):
             ma.perform()
         return self
 
-    def swipe(self, start_x, start_y, end_x, end_y, duration=None):
+    def swipe(self, start_x: int, start_y: int, end_x: int, end_y: int, duration: int = 0) -> T:
         """Swipe from one point to another point, for an optional duration.
 
         Args:
@@ -127,7 +132,7 @@ def swipe(self, start_x, start_y, end_x, end_y, duration=None):
         action.perform()
         return self
 
-    def flick(self, start_x, start_y, end_x, end_y):
+    def flick(self, start_x: int, start_y: int, end_x: int, end_y: int) -> T:
         """Flick from one point to another point.
 
         Args:
diff --git a/appium/webdriver/extensions/android/activities.py b/appium/webdriver/extensions/android/activities.py
index 236252c3..f80805a0 100644
--- a/appium/webdriver/extensions/android/activities.py
+++ b/appium/webdriver/extensions/android/activities.py
@@ -12,15 +12,19 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import TypeVar
+
 from selenium import webdriver
 from selenium.common.exceptions import TimeoutException
 from selenium.webdriver.support.ui import WebDriverWait
 
 from appium.webdriver.mobilecommand import MobileCommand as Command
 
+T = TypeVar('T', bound='Activities')
+
 
 class Activities(webdriver.Remote):
-    def start_activity(self, app_package, app_activity, **opts):
+    def start_activity(self, app_package: str, app_activity: str, **opts: str) -> T:
         """Opens an arbitrary activity during a test. If the activity belongs to
         another application, that application is started and the activity is opened.
 
@@ -59,7 +63,7 @@ def start_activity(self, app_package, app_activity, **opts):
         return self
 
     @property
-    def current_activity(self):
+    def current_activity(self) -> str:
         """Retrieves the current activity running on the device.
 
         Returns:
@@ -67,7 +71,7 @@ def current_activity(self):
         """
         return self.execute(Command.GET_CURRENT_ACTIVITY)['value']
 
-    def wait_activity(self, activity, timeout, interval=1):
+    def wait_activity(self, activity: str, timeout: int, interval: int = 1) -> bool:
         """Wait for an activity: block until target activity presents or time out.
 
         This is an Android-only method.
@@ -76,6 +80,9 @@ def wait_activity(self, activity, timeout, interval=1):
             activity (str): target activity
             timeout (int): max wait time, in seconds
             interval (int): sleep interval between retries, in seconds
+
+        Returns:
+            bool: `True` if the target activity is shown
         """
         try:
             WebDriverWait(self, timeout, interval).until(
@@ -86,7 +93,7 @@ def wait_activity(self, activity, timeout, interval=1):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.GET_CURRENT_ACTIVITY] = \
             ('GET', '/session/$sessionId/appium/device/current_activity')
         self.command_executor._commands[Command.START_ACTIVITY] = \
diff --git a/appium/webdriver/extensions/android/common.py b/appium/webdriver/extensions/android/common.py
index 4fa3a00f..65da6733 100644
--- a/appium/webdriver/extensions/android/common.py
+++ b/appium/webdriver/extensions/android/common.py
@@ -12,14 +12,18 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Any, TypeVar
+
 from selenium import webdriver
 
 from appium.webdriver.mobilecommand import MobileCommand as Command
 
+T = TypeVar('T', bound='Common')
+
 
 class Common(webdriver.Remote):
 
-    def end_test_coverage(self, intent, path):
+    def end_test_coverage(self, intent: str, path: str) -> Any:  # TODO Check return type
         """Ends the coverage collection and pull the coverage.ec file from the device.
 
         Android only.
@@ -38,7 +42,7 @@ def end_test_coverage(self, intent, path):
         }
         return self.execute(Command.END_TEST_COVERAGE, data)['value']
 
-    def open_notifications(self):
+    def open_notifications(self) -> T:
         """Open notification shade in Android (API Level 18 and above)
 
         Returns:
@@ -48,12 +52,12 @@ def open_notifications(self):
         return self
 
     @property
-    def current_package(self):
+    def current_package(self) -> str:
         """Retrieves the current package running on the device.
         """
         return self.execute(Command.GET_CURRENT_PACKAGE)['value']
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.GET_CURRENT_PACKAGE] = \
             ('GET', '/session/$sessionId/appium/device/current_package')
         self.command_executor._commands[Command.END_TEST_COVERAGE] = \
diff --git a/appium/webdriver/extensions/android/display.py b/appium/webdriver/extensions/android/display.py
index c05e1a5d..73ac1ccb 100644
--- a/appium/webdriver/extensions/android/display.py
+++ b/appium/webdriver/extensions/android/display.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import TypeVar
+
 from selenium import webdriver
 
 from appium.webdriver.mobilecommand import MobileCommand as Command
@@ -19,7 +21,7 @@
 
 class Display(webdriver.Remote):
 
-    def get_display_density(self):
+    def get_display_density(self) -> int:
         """Get the display density, Android only
 
         Returns:
@@ -32,6 +34,6 @@ def get_display_density(self):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.GET_DISPLAY_DENSITY] = \
             ('GET', '/session/$sessionId/appium/device/display_density')
diff --git a/appium/webdriver/extensions/android/gsm.py b/appium/webdriver/extensions/android/gsm.py
index 4aaf4fc8..df4ea95e 100644
--- a/appium/webdriver/extensions/android/gsm.py
+++ b/appium/webdriver/extensions/android/gsm.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import TypeVar
+
 from selenium import webdriver
 
 from appium.common.helper import extract_const_attributes
@@ -44,9 +46,12 @@ class GsmVoiceState(object):
     ON = 'on'
 
 
+T = TypeVar('T', bound='Gsm')
+
+
 class Gsm(webdriver.Remote):
 
-    def make_gsm_call(self, phone_number, action):
+    def make_gsm_call(self, phone_number: str, action: str) -> T:
         """Make GSM call (Emulator only)
 
         Android only.
@@ -66,7 +71,7 @@ def make_gsm_call(self, phone_number, action):
         self.execute(Command.MAKE_GSM_CALL, {'phoneNumber': phone_number, 'action': action})
         return self
 
-    def set_gsm_signal(self, strength):
+    def set_gsm_signal(self, strength: int) -> T:
         """Set GSM signal strength (Emulator only)
 
         Android only.
@@ -85,7 +90,7 @@ def set_gsm_signal(self, strength):
         self.execute(Command.SET_GSM_SIGNAL, {'signalStrength': strength, 'signalStrengh': strength})
         return self
 
-    def set_gsm_voice(self, state):
+    def set_gsm_voice(self, state: str) -> T:
         """Set GSM voice state (Emulator only)
 
         Android only.
@@ -106,7 +111,7 @@ def set_gsm_voice(self, state):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.MAKE_GSM_CALL] = \
             ('POST', '/session/$sessionId/appium/device/gsm_call')
         self.command_executor._commands[Command.SET_GSM_SIGNAL] = \
diff --git a/appium/webdriver/extensions/android/nativekey.py b/appium/webdriver/extensions/android/nativekey.py
index aca374eb..79973dba 100644
--- a/appium/webdriver/extensions/android/nativekey.py
+++ b/appium/webdriver/extensions/android/nativekey.py
@@ -1,3 +1,18 @@
+#!/usr/bin/env python
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
 class AndroidKey:
     # Key code constant: Unknown key code.
     UNKNOWN = 0
@@ -1005,14 +1020,14 @@ class AndroidKey:
                        BUTTON_15, BUTTON_16]
 
     @staticmethod
-    def is_gamepad_button(code):
+    def is_gamepad_button(code: int) -> bool:
         """Returns true if the specified nativekey is a gamepad button."""
         return code in AndroidKey.gamepad_buttons
 
     confirm_buttons = [DPAD_CENTER, ENTER, SPACE, NUMPAD_ENTER]
 
     @staticmethod
-    def is_confirm_key(code):
+    def is_confirm_key(code: int) -> bool:
         """Returns true if the key will, by default, trigger a click on the focused view."""
         return code in AndroidKey.confirm_buttons
 
@@ -1021,7 +1036,7 @@ def is_confirm_key(code):
                      MEDIA_REWIND, MEDIA_RECORD, MEDIA_FAST_FORWARD]
 
     @staticmethod
-    def is_media_key(code):
+    def is_media_key(code: int) -> bool:
         """Returns true if this key is a media key, which can be send to apps that are
         interested in media key events."""
         return code in AndroidKey.media_buttons
@@ -1035,13 +1050,13 @@ def is_media_key(code):
                       BRIGHTNESS_DOWN, BRIGHTNESS_UP, MEDIA_AUDIO_TRACK]
 
     @staticmethod
-    def is_system_key(code):
+    def is_system_key(code: int) -> bool:
         """Returns true if the key is a system key, System keys can not be used for menu shortcuts."""
         return code in AndroidKey.system_buttons
 
     wake_buttons = [BACK, MENU, WAKEUP, PAIRING, STEM_1, STEM_2, STEM_3]
 
     @staticmethod
-    def is_wake_key(code):
+    def is_wake_key(code: int) -> bool:
         """Returns true if the key is a wake key."""
         return code in AndroidKey.wake_buttons
diff --git a/appium/webdriver/extensions/android/network.py b/appium/webdriver/extensions/android/network.py
index 3a648154..99c71763 100644
--- a/appium/webdriver/extensions/android/network.py
+++ b/appium/webdriver/extensions/android/network.py
@@ -12,12 +12,16 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Any, TypeVar
+
 from selenium import webdriver
 
 from appium.common.helper import extract_const_attributes
 from appium.common.logger import logger
 from appium.webdriver.mobilecommand import MobileCommand as Command
 
+T = TypeVar('T', bound='Network')
+
 
 class NetSpeed(object):
     GSM = 'gsm'  # GSM/CSD (up: 14.4(kbps), down: 14.4(kbps))
@@ -34,7 +38,7 @@ class NetSpeed(object):
 class Network(webdriver.Remote):
 
     @property
-    def network_connection(self):
+    def network_connection(self) -> int:
         """Returns an integer bitmask specifying the network connection type.
 
         Android only.
@@ -42,7 +46,7 @@ def network_connection(self):
         """
         return self.execute(Command.GET_NETWORK_CONNECTION, {})['value']
 
-    def set_network_connection(self, connection_type):
+    def set_network_connection(self, connection_type: int) -> int:
         """Sets the network connection type. Android only.
 
         Possible values:
@@ -58,8 +62,8 @@ def set_network_connection(self, connection_type):
         Args:
             connection_type (int): a member of the enum appium.webdriver.ConnectionType
 
-        Returns:
-            `appium.webdriver.webdriver.WebDriver`
+        Return:
+            int: Set network connection type
         """
         data = {
             'parameters': {
@@ -68,7 +72,7 @@ def set_network_connection(self, connection_type):
         }
         return self.execute(Command.SET_NETWORK_CONNECTION, data)['value']
 
-    def toggle_wifi(self):
+    def toggle_wifi(self) -> T:
         """Toggle the wifi on the device, Android only.
 
         Returns:
@@ -77,7 +81,7 @@ def toggle_wifi(self):
         self.execute(Command.TOGGLE_WIFI, {})
         return self
 
-    def set_network_speed(self, speed_type):
+    def set_network_speed(self, speed_type: str) -> T:
         """Set the network speed emulation.
 
         Android Emulator only.
@@ -102,7 +106,7 @@ def set_network_speed(self, speed_type):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.TOGGLE_WIFI] = \
             ('POST', '/session/$sessionId/appium/device/toggle_wifi')
         self.command_executor._commands[Command.GET_NETWORK_CONNECTION] = \
diff --git a/appium/webdriver/extensions/android/performance.py b/appium/webdriver/extensions/android/performance.py
index 7b77b74e..3d661d77 100644
--- a/appium/webdriver/extensions/android/performance.py
+++ b/appium/webdriver/extensions/android/performance.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Dict, List, Union
+
 from selenium import webdriver
 
 from appium.webdriver.mobilecommand import MobileCommand as Command
@@ -19,7 +21,7 @@
 
 class Performance(webdriver.Remote):
 
-    def get_performance_data(self, package_name, data_type, data_read_timeout=None):
+    def get_performance_data(self, package_name: str, data_type: str, data_read_timeout: int = None) -> List[List[str]]:
         """Returns the information of the system state
         which is supported to read as like cpu, memory, network traffic, and battery.
 
@@ -36,14 +38,14 @@ def get_performance_data(self, package_name, data_type, data_read_timeout=None):
             self.driver.get_performance_data('my.app.package', 'cpuinfo', 5)
 
         Returns:
-            dict: The data along to `data_type`
+            list: The data along to `data_type`
         """
-        data = {'packageName': package_name, 'dataType': data_type}
+        data: Dict[str, Union[str, int]] = {'packageName': package_name, 'dataType': data_type}
         if data_read_timeout is not None:
             data['dataReadTimeout'] = data_read_timeout
         return self.execute(Command.GET_PERFORMANCE_DATA, data)['value']
 
-    def get_performance_data_types(self):
+    def get_performance_data_types(self) -> List:
         """Returns the information types of the system state
         which is supported to read as like cpu, memory, network traffic, and battery.
         Android only.
@@ -58,7 +60,7 @@ def get_performance_data_types(self):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.GET_PERFORMANCE_DATA] = \
             ('POST', '/session/$sessionId/appium/getPerformanceData')
         self.command_executor._commands[Command.GET_PERFORMANCE_DATA_TYPES] = \
diff --git a/appium/webdriver/extensions/android/power.py b/appium/webdriver/extensions/android/power.py
index bfa6a824..827324e8 100644
--- a/appium/webdriver/extensions/android/power.py
+++ b/appium/webdriver/extensions/android/power.py
@@ -12,16 +12,20 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import TypeVar
+
 from selenium import webdriver
 
 from appium.webdriver.mobilecommand import MobileCommand as Command
 
+T = TypeVar('T', bound='Power')
+
 
 class Power(webdriver.Remote):
 
     AC_OFF, AC_ON = 'off', 'on'
 
-    def set_power_capacity(self, percent):
+    def set_power_capacity(self, percent: int) -> T:
         """Emulate power capacity change on the connected emulator.
 
         Android only.
@@ -38,7 +42,7 @@ def set_power_capacity(self, percent):
         self.execute(Command.SET_POWER_CAPACITY, {'percent': percent})
         return self
 
-    def set_power_ac(self, ac_state):
+    def set_power_ac(self, ac_state: str) -> T:
         """Emulate power state change on the connected emulator.
 
         Android only.
@@ -58,7 +62,7 @@ def set_power_ac(self, ac_state):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.SET_POWER_CAPACITY] = \
             ('POST', '/session/$sessionId/appium/device/power_capacity')
         self.command_executor._commands[Command.SET_POWER_AC] = \
diff --git a/appium/webdriver/extensions/android/sms.py b/appium/webdriver/extensions/android/sms.py
index 4c0675a0..8f7773cf 100644
--- a/appium/webdriver/extensions/android/sms.py
+++ b/appium/webdriver/extensions/android/sms.py
@@ -12,14 +12,18 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import TypeVar
+
 from selenium import webdriver
 
 from appium.webdriver.mobilecommand import MobileCommand as Command
 
+T = TypeVar('T', bound='Sms')
+
 
 class Sms(webdriver.Remote):
 
-    def send_sms(self, phone_number, message):
+    def send_sms(self, phone_number: str, message: str) -> T:
         """Emulate send SMS event on the connected emulator.
 
         Android only.
@@ -39,6 +43,6 @@ def send_sms(self, phone_number, message):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.SEND_SMS] = \
             ('POST', '/session/$sessionId/appium/device/send_sms')
diff --git a/appium/webdriver/extensions/android/system_bars.py b/appium/webdriver/extensions/android/system_bars.py
index edc98a5e..085296d9 100644
--- a/appium/webdriver/extensions/android/system_bars.py
+++ b/appium/webdriver/extensions/android/system_bars.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Dict, Union
+
 from selenium import webdriver
 
 from appium.webdriver.mobilecommand import MobileCommand as Command
@@ -19,7 +21,7 @@
 
 class SystemBars(webdriver.Remote):
 
-    def get_system_bars(self):
+    def get_system_bars(self) -> Dict[str, Dict[str, Union[int, bool]]]:
         """Retrieve visibility and bounds information of the status and navigation bars.
 
         Android only.
@@ -43,6 +45,6 @@ def get_system_bars(self):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.GET_SYSTEM_BARS] = \
             ('GET', '/session/$sessionId/appium/device/system_bars')
diff --git a/appium/webdriver/extensions/applications.py b/appium/webdriver/extensions/applications.py
index e89b097d..9ab8a295 100644
--- a/appium/webdriver/extensions/applications.py
+++ b/appium/webdriver/extensions/applications.py
@@ -12,13 +12,17 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Any, Dict, TypeVar
+
 from selenium import webdriver
 
 from ..mobilecommand import MobileCommand as Command
 
+T = TypeVar('T', bound='Applications')
+
 
 class Applications(webdriver.Remote):
-    def background_app(self, seconds):
+    def background_app(self, seconds: int) -> T:
         """Puts the application in the background on the device for a certain duration.
 
         Args:
@@ -33,7 +37,7 @@ def background_app(self, seconds):
         self.execute(Command.BACKGROUND, data)
         return self
 
-    def is_app_installed(self, bundle_id):
+    def is_app_installed(self, bundle_id: str) -> bool:
         """Checks whether the application specified by `bundle_id` is installed on the device.
 
         Args:
@@ -47,7 +51,7 @@ def is_app_installed(self, bundle_id):
         }
         return self.execute(Command.IS_APP_INSTALLED, data)['value']
 
-    def install_app(self, app_path, **options):
+    def install_app(self, app_path: str, **options: Any) -> T:
         """Install the application found at `app_path` on the device.
 
         Args:
@@ -67,7 +71,7 @@ def install_app(self, app_path, **options):
         Returns:
             `appium.webdriver.webdriver.WebDriver`
         """
-        data = {
+        data: Dict[str, Any] = {
             'appPath': app_path,
         }
         if options:
@@ -75,7 +79,7 @@ def install_app(self, app_path, **options):
         self.execute(Command.INSTALL_APP, data)
         return self
 
-    def remove_app(self, app_id, **options):
+    def remove_app(self, app_id: str, **options: Any) -> T:
         """Remove the specified application from the device.
 
         Args:
@@ -90,7 +94,7 @@ def remove_app(self, app_id, **options):
         Returns:
             `appium.webdriver.webdriver.WebDriver`
         """
-        data = {
+        data: Dict[str, Any] = {
             'appId': app_id,
         }
         if options:
@@ -98,7 +102,7 @@ def remove_app(self, app_id, **options):
         self.execute(Command.REMOVE_APP, data)
         return self
 
-    def launch_app(self):
+    def launch_app(self) -> T:
         """Start on the device the application specified in the desired capabilities.
 
         Returns:
@@ -107,7 +111,7 @@ def launch_app(self):
         self.execute(Command.LAUNCH_APP)
         return self
 
-    def close_app(self):
+    def close_app(self) -> T:
         """Stop the running application, specified in the desired capabilities, on
         the device.
 
@@ -117,7 +121,7 @@ def close_app(self):
         self.execute(Command.CLOSE_APP)
         return self
 
-    def terminate_app(self, app_id, **options):
+    def terminate_app(self, app_id: str, **options: Any) -> bool:
         """Terminates the application if it is running.
 
         Args:
@@ -130,14 +134,14 @@ def terminate_app(self, app_id, **options):
         Returns:
             bool: True if the app has been successfully terminated
         """
-        data = {
+        data: Dict[str, Any] = {
             'appId': app_id,
         }
         if options:
             data.update({'options': options})
         return self.execute(Command.TERMINATE_APP, data)['value']
 
-    def activate_app(self, app_id):
+    def activate_app(self, app_id: str) -> T:
         """Activates the application if it is not running
         or is running in the background.
 
@@ -153,7 +157,7 @@ def activate_app(self, app_id):
         self.execute(Command.ACTIVATE_APP, data)
         return self
 
-    def query_app_state(self, app_id):
+    def query_app_state(self, app_id: str) -> int:
         """Queries the state of the application.
 
         Args:
@@ -168,7 +172,7 @@ class for more details.
         }
         return self.execute(Command.QUERY_APP_STATE, data)['value']
 
-    def app_strings(self, language=None, string_file=None):
+    def app_strings(self, language: str = None, string_file: str = None) -> str:
         """Returns the application strings from the device for the specified
         language.
 
@@ -183,7 +187,7 @@ def app_strings(self, language=None, string_file=None):
             data['stringFile'] = string_file
         return self.execute(Command.GET_APP_STRINGS, data)['value']
 
-    def reset(self):
+    def reset(self) -> T:
         """Resets the current application on the device.
         """
         self.execute(Command.RESET)
@@ -191,7 +195,7 @@ def reset(self):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.BACKGROUND] = \
             ('POST', '/session/$sessionId/appium/app/background')
         self.command_executor._commands[Command.IS_APP_INSTALLED] = \
diff --git a/appium/webdriver/extensions/clipboard.py b/appium/webdriver/extensions/clipboard.py
index e05e6b86..e4f7bc71 100644
--- a/appium/webdriver/extensions/clipboard.py
+++ b/appium/webdriver/extensions/clipboard.py
@@ -13,25 +13,31 @@
 # limitations under the License.
 
 import base64
+from typing import Any, Dict, Optional, TypeVar
 
 from selenium import webdriver
 
-from appium.common.helper import appium_bytes
 from appium.webdriver.clipboard_content_type import ClipboardContentType
 
 from ..mobilecommand import MobileCommand as Command
 
+T = TypeVar('T', bound='Clipboard')
+
 
 class Clipboard(webdriver.Remote):
 
-    def set_clipboard(self, content, content_type=ClipboardContentType.PLAINTEXT, label=None):
+    def set_clipboard(self, content: bytes, content_type: str = ClipboardContentType.PLAINTEXT,
+                      label: Optional[str] = None) -> T:
         """Set the content of the system clipboard
 
         Args:
-            content (str): The content to be set as bytearray string
+            content (bytes): The content to be set as bytearray string
             content_type (str): One of ClipboardContentType items. Only ClipboardContentType.PLAINTEXT
                 is supported on Android
             label (:obj:`str`, optional): label argument, which only works for Android
+
+        Returns:
+            `appium.webdriver.webdriver.WebDriver`
         """
         options = {
             'content': base64.b64encode(content).decode('UTF-8'),
@@ -40,18 +46,23 @@ def set_clipboard(self, content, content_type=ClipboardContentType.PLAINTEXT, la
         if label:
             options['label'] = label
         self.execute(Command.SET_CLIPBOARD, options)
+        return self
 
-    def set_clipboard_text(self, text, label=None):
+    def set_clipboard_text(self, text: str, label: Optional[str] = None) -> T:
         """Copies the given text to the system clipboard
 
         Args:
             text (str): The text to be set
-            label (:obj:`int`, optional):label argument, which only works for Android
+            label (:obj:`str`, optional):label argument, which only works for Android
+
+        Returns:
+            `appium.webdriver.webdriver.WebDriver`
         """
 
-        self.set_clipboard(appium_bytes(str(text), 'UTF-8'), ClipboardContentType.PLAINTEXT, label)
+        self.set_clipboard(bytes(str(text), 'UTF-8'), ClipboardContentType.PLAINTEXT, label)
+        return self
 
-    def get_clipboard(self, content_type=ClipboardContentType.PLAINTEXT):
+    def get_clipboard(self, content_type: str = ClipboardContentType.PLAINTEXT) -> bytes:
         """Receives the content of the system clipboard
 
         Args:
@@ -66,7 +77,7 @@ def get_clipboard(self, content_type=ClipboardContentType.PLAINTEXT):
         })['value']
         return base64.b64decode(base64_str)
 
-    def get_clipboard_text(self):
+    def get_clipboard_text(self) -> str:
         """Receives the text of the system clipboard
 
         Return:
@@ -76,7 +87,7 @@ def get_clipboard_text(self):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.SET_CLIPBOARD] = \
             ('POST', '/session/$sessionId/appium/device/set_clipboard')
         self.command_executor._commands[Command.GET_CLIPBOARD] = \
diff --git a/appium/webdriver/extensions/context.py b/appium/webdriver/extensions/context.py
index 8581cc3f..9ff5ec62 100644
--- a/appium/webdriver/extensions/context.py
+++ b/appium/webdriver/extensions/context.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import List
+
 from selenium import webdriver
 
 from ..mobilecommand import MobileCommand as Command
@@ -19,7 +21,7 @@
 
 class Context(webdriver.Remote):
     @property
-    def contexts(self):
+    def contexts(self) -> List[str]:
         """Returns the contexts within the current session.
 
         Usage:
@@ -32,7 +34,7 @@ def contexts(self):
         return self.execute(Command.CONTEXTS)['value']
 
     @property
-    def current_context(self):
+    def current_context(self) -> str:
         """Returns the current context of the current session.
 
         Usage:
@@ -44,7 +46,7 @@ def current_context(self):
         return self.execute(Command.GET_CURRENT_CONTEXT)['value']
 
     @property
-    def context(self):
+    def context(self) -> str:
         """Returns the current context of the current session.
 
         Usage:
@@ -57,7 +59,7 @@ def context(self):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.CONTEXTS] = \
             ('GET', '/session/$sessionId/contexts')
         self.command_executor._commands[Command.GET_CURRENT_CONTEXT] = \
diff --git a/appium/webdriver/extensions/device_time.py b/appium/webdriver/extensions/device_time.py
index e40b36d2..d16f56b3 100644
--- a/appium/webdriver/extensions/device_time.py
+++ b/appium/webdriver/extensions/device_time.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Optional
+
 from selenium import webdriver
 
 from ..mobilecommand import MobileCommand as Command
@@ -20,7 +22,7 @@
 class DeviceTime(webdriver.Remote):
 
     @property
-    def device_time(self):
+    def device_time(self) -> str:
         """Returns the date and time from the device.
 
         Return:
@@ -28,11 +30,11 @@ def device_time(self):
         """
         return self.execute(Command.GET_DEVICE_TIME_GET, {})['value']
 
-    def get_device_time(self, format=None):
+    def get_device_time(self, format: Optional[str] = None) -> str:
         """Returns the date and time from the device.
 
         Args:
-            format (optional):  The set of format specifiers. Read https://momentjs.com/docs/
+            format (:obj:`str`, optional):  The set of format specifiers. Read https://momentjs.com/docs/
                 to get the full list of supported datetime format specifiers.
                 If unset, return :func:`.device_time` as default format is `YYYY-MM-DDTHH:mm:ssZ`,
                 which complies to ISO-8601
@@ -50,7 +52,7 @@ def get_device_time(self, format=None):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.GET_DEVICE_TIME_GET] = \
             ('GET', '/session/$sessionId/appium/device/system_time')
         self.command_executor._commands[Command.GET_DEVICE_TIME_POST] = \
diff --git a/appium/webdriver/extensions/execute_driver.py b/appium/webdriver/extensions/execute_driver.py
index 5c866a39..f6c00fb0 100644
--- a/appium/webdriver/extensions/execute_driver.py
+++ b/appium/webdriver/extensions/execute_driver.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Any, Dict, Optional, Union
+
 from selenium import webdriver
 
 from ..mobilecommand import MobileCommand as Command
@@ -19,15 +21,16 @@
 
 class ExecuteDriver(webdriver.Remote):
 
-    def execute_driver(self, script, script_type='webdriverio', timeout_ms=None):
+    # TODO Inner class case
+    def execute_driver(self, script: str, script_type: str = 'webdriverio', timeout_ms: Optional[int] = None) -> Any:
         """Run a set of script against the current session, allowing execution of many commands in one Appium request.
         Please read http://appium.io/docs/en/commands/session/execute-driver for more details about the acceptable
         scripts and the output format.
 
         Args:
-            script (string): The string consisting of the script itself
-            script_type (string): The name of the script type. Defaults to 'webdriverio'.
-            timeout_ms (optional): The number of `ms` Appium should wait for the script to finish before killing it due to timeout_ms.
+            script (str): The string consisting of the script itself
+            script_type (str): The name of the script type. Defaults to 'webdriverio'.
+            timeout_ms (:obj:`int`, optional): The number of `ms` Appium should wait for the script to finish before killing it due to timeout_ms.
 
         Usage:
             self.driver.execute_driver(script='return [];')
@@ -43,11 +46,11 @@ def execute_driver(self, script, script_type='webdriverio', timeout_ms=None):
 
         class Result(object):
 
-            def __init__(self, response):
+            def __init__(self, response: Dict):
                 self.result = response['result']
                 self.logs = response['logs']
 
-        option = {'script': script, 'type': script_type}
+        option: Dict[str, Union[str, int]] = {'script': script, 'type': script_type}
         if timeout_ms is not None:
             option['timeout'] = timeout_ms
 
@@ -56,6 +59,6 @@ def __init__(self, response):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.EXECUTE_DRIVER] = \
             ('POST', '/session/$sessionId/appium/execute_driver')
diff --git a/appium/webdriver/extensions/execute_mobile_command.py b/appium/webdriver/extensions/execute_mobile_command.py
index 789dcfef..9866df7f 100644
--- a/appium/webdriver/extensions/execute_mobile_command.py
+++ b/appium/webdriver/extensions/execute_mobile_command.py
@@ -12,12 +12,16 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Any, Dict, TypeVar
+
 from selenium import webdriver
 
+T = TypeVar('T', bound='ExecuteMobileCommand')
+
 
 class ExecuteMobileCommand(webdriver.Remote):
 
-    def press_button(self, button_name):
+    def press_button(self, button_name: str) -> T:
         """Sends a physical button name to the device to simulate the user pressing.
 
         iOS only.
@@ -38,7 +42,7 @@ def press_button(self, button_name):
         return self
 
     @property
-    def battery_info(self):
+    def battery_info(self) -> Dict[str, Any]:
         """Retrieves battery information for the device under test.
 
         Returns:
diff --git a/appium/webdriver/extensions/hw_actions.py b/appium/webdriver/extensions/hw_actions.py
index a3d6babb..c27c7382 100644
--- a/appium/webdriver/extensions/hw_actions.py
+++ b/appium/webdriver/extensions/hw_actions.py
@@ -12,18 +12,22 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Any, Optional, TypeVar
+
 from selenium import webdriver
 
 from ..mobilecommand import MobileCommand as Command
 
+T = TypeVar('T', bound='HardwareActions')
+
 
 class HardwareActions(webdriver.Remote):
 
-    def lock(self, seconds=None):
+    def lock(self, seconds: Optional[int] = None) -> T:
         """Lock the device. No changes are made if the device is already unlocked.
 
         Args:
-            seconds (optional): The duration to lock the device, in seconds.
+            seconds (:obj:`int`, optional): The duration to lock the device, in seconds.
                 The device is going to be locked forever until `unlock` is called
                 if it equals or is less than zero, otherwise this call blocks until
                 the timeout expires and unlocks the screen automatically.
@@ -38,7 +42,7 @@ def lock(self, seconds=None):
 
         return self
 
-    def unlock(self):
+    def unlock(self) -> T:
         """Unlock the device. No changes are made if the device is already locked.
 
         Returns:
@@ -47,7 +51,7 @@ def unlock(self):
         self.execute(Command.UNLOCK)
         return self
 
-    def is_locked(self):
+    def is_locked(self) -> bool:
         """Checks whether the device is locked.
 
         Returns:
@@ -55,7 +59,7 @@ def is_locked(self):
         """
         return self.execute(Command.IS_LOCKED)['value']
 
-    def shake(self):
+    def shake(self) -> T:
         """Shake the device.
 
         Returns:
@@ -64,7 +68,7 @@ def shake(self):
         self.execute(Command.SHAKE)
         return self
 
-    def touch_id(self, match):
+    def touch_id(self, match: bool) -> T:
         """Simulate touchId on iOS Simulator
 
         Args:
@@ -79,7 +83,7 @@ def touch_id(self, match):
         self.execute(Command.TOUCH_ID, data)
         return self
 
-    def toggle_touch_id_enrollment(self):
+    def toggle_touch_id_enrollment(self) -> T:
         """Toggle enroll touchId on iOS Simulator
 
         Returns:
@@ -88,7 +92,7 @@ def toggle_touch_id_enrollment(self):
         self.execute(Command.TOGGLE_TOUCH_ID_ENROLLMENT)
         return self
 
-    def finger_print(self, finger_id):
+    def finger_print(self, finger_id: int) -> Any:
         """Authenticate users by using their finger print scans on supported Android emulators.
 
         Args:
@@ -101,7 +105,7 @@ def finger_print(self, finger_id):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.LOCK] = \
             ('POST', '/session/$sessionId/appium/device/lock')
         self.command_executor._commands[Command.UNLOCK] = \
diff --git a/appium/webdriver/extensions/images_comparison.py b/appium/webdriver/extensions/images_comparison.py
index c0f16a90..77289fe8 100644
--- a/appium/webdriver/extensions/images_comparison.py
+++ b/appium/webdriver/extensions/images_comparison.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Any, Dict, Union
+
 from selenium import webdriver
 
 from ..mobilecommand import MobileCommand as Command
@@ -19,7 +21,7 @@
 
 class ImagesComparison(webdriver.Remote):
 
-    def match_images_features(self, base64_image1, base64_image2, **opts):
+    def match_images_features(self, base64_image1: bytes, base64_image2: bytes, **opts: Any) -> Dict[str, Any]:
         """Performs images matching by features.
 
         Read
@@ -73,7 +75,8 @@ def match_images_features(self, base64_image1, base64_image2, **opts):
         }
         return self.execute(Command.COMPARE_IMAGES, options)['value']
 
-    def find_image_occurrence(self, base64_full_image, base64_partial_image, **opts):
+    def find_image_occurrence(self, base64_full_image: bytes, base64_partial_image: bytes,
+                              **opts: Any) -> Dict[str, Union[bytes, Dict]]:
         """Performs images matching by template to find possible occurrence of the partial image
         in the full image.
 
@@ -91,10 +94,11 @@ def find_image_occurrence(self, base64_full_image, base64_partial_image, **opts)
                 False by default
 
         Returns:
-            visualization (bytes): base64-encoded content of PNG visualization of the current comparison
-                operation. This entry is only present if `visualize` option is enabled
-            rect (dict): The region of the partial image occurrence on the full image.
-                The rect is represented by a dictionary with 'x', 'y', 'width' and 'height' keys
+            The dictionary containing the following entries:
+                visualization (bytes): base64-encoded content of PNG visualization of the current comparison
+                    operation. This entry is only present if `visualize` option is enabled
+                rect (dict): The region of the partial image occurrence on the full image.
+                    The rect is represented by a dictionary with 'x', 'y', 'width' and 'height' keys
         """
         options = {
             'mode': 'matchTemplate',
@@ -104,7 +108,8 @@ def find_image_occurrence(self, base64_full_image, base64_partial_image, **opts)
         }
         return self.execute(Command.COMPARE_IMAGES, options)['value']
 
-    def get_images_similarity(self, base64_image1, base64_image2, **opts):
+    def get_images_similarity(self, base64_image1: bytes, base64_image2: bytes,
+                              **opts: Any) -> Dict[str, Union[bytes, Dict]]:
         """Performs images matching to calculate the similarity score between them.
 
         The flow there is similar to the one used in
@@ -120,10 +125,11 @@ def get_images_similarity(self, base64_image1, base64_image2, **opts):
                 False by default
 
         Returns:
-            visualization (bytes): base64-encoded content of PNG visualization of the current comparison
-                operation. This entry is only present if `visualize` option is enabled
-            score (float): The similarity score as a float number in range [0.0, 1.0].
-                1.0 is the highest score (means both images are totally equal).
+            The dictionary containing the following entries:
+                visualization (bytes): base64-encoded content of PNG visualization of the current comparison
+                    operation. This entry is only present if `visualize` option is enabled
+                score (float): The similarity score as a float number in range [0.0, 1.0].
+                    1.0 is the highest score (means both images are totally equal).
         """
         options = {
             'mode': 'getSimilarity',
@@ -135,6 +141,6 @@ def get_images_similarity(self, base64_image1, base64_image2, **opts):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.COMPARE_IMAGES] = \
             ('POST', '/session/$sessionId/appium/compare_images')
diff --git a/appium/webdriver/extensions/ime.py b/appium/webdriver/extensions/ime.py
index 9c3230e3..701c4f5c 100644
--- a/appium/webdriver/extensions/ime.py
+++ b/appium/webdriver/extensions/ime.py
@@ -12,15 +12,19 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import List, TypeVar
+
 from selenium import webdriver
 
 from ..mobilecommand import MobileCommand as Command
 
+T = TypeVar('T', bound='IME')
+
 
 class IME(webdriver.Remote):
 
     @property
-    def available_ime_engines(self):
+    def available_ime_engines(self) -> List[str]:
         """Get the available input methods for an Android device.
 
         Package and activity are returned (e.g., ['com.android.inputmethod.latin/.LatinIME'])
@@ -31,7 +35,7 @@ def available_ime_engines(self):
         """
         return self.execute(Command.GET_AVAILABLE_IME_ENGINES, {})['value']
 
-    def is_ime_active(self):
+    def is_ime_active(self) -> bool:
         """Checks whether the device has IME service active.
         Android only.
 
@@ -40,7 +44,7 @@ def is_ime_active(self):
         """
         return self.execute(Command.IS_IME_ACTIVE, {})['value']
 
-    def activate_ime_engine(self, engine):
+    def activate_ime_engine(self, engine: str) -> T:
         """Activates the given IME engine on the device.
 
         Android only.
@@ -58,7 +62,7 @@ def activate_ime_engine(self, engine):
         self.execute(Command.ACTIVATE_IME_ENGINE, data)
         return self
 
-    def deactivate_ime_engine(self):
+    def deactivate_ime_engine(self) -> T:
         """Deactivates the currently active IME engine on the device.
 
         Android only.
@@ -70,7 +74,7 @@ def deactivate_ime_engine(self):
         return self
 
     @property
-    def active_ime_engine(self):
+    def active_ime_engine(self) -> str:
         """Returns the activity and package of the currently active IME engine(e.g., 'com.android.inputmethod.latin/.LatinIME').
 
         Android only.
@@ -82,7 +86,7 @@ def active_ime_engine(self):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.GET_AVAILABLE_IME_ENGINES] = \
             ('GET', '/session/$sessionId/ime/available_engines')
         self.command_executor._commands[Command.IS_IME_ACTIVE] = \
diff --git a/appium/webdriver/extensions/keyboard.py b/appium/webdriver/extensions/keyboard.py
index 612a99b6..029996fc 100644
--- a/appium/webdriver/extensions/keyboard.py
+++ b/appium/webdriver/extensions/keyboard.py
@@ -12,14 +12,19 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Dict, Optional, TypeVar
+
 from selenium import webdriver
 
 from ..mobilecommand import MobileCommand as Command
 
+T = TypeVar('T', bound='Keyboard')
+
 
 class Keyboard(webdriver.Remote):
 
-    def hide_keyboard(self, key_name=None, key=None, strategy=None):
+    def hide_keyboard(self, key_name: Optional[str] = None, key: Optional[str]
+                      = None, strategy: Optional[str] = None) -> T:
         """Hides the software keyboard on the device.
 
         In iOS, use `key_name` to press
@@ -30,7 +35,7 @@ def hide_keyboard(self, key_name=None, key=None, strategy=None):
             key (:obj:`str`, optional):
             strategy (:obj:`str`, optional): strategy for closing the keyboard (e.g., `tapOutside`)
         """
-        data = {}
+        data: Dict[str, Optional[str]] = {}
         if key_name is not None:
             data['keyName'] = key_name
         elif key is not None:
@@ -41,7 +46,7 @@ def hide_keyboard(self, key_name=None, key=None, strategy=None):
         self.execute(Command.HIDE_KEYBOARD, data)
         return self
 
-    def is_keyboard_shown(self):
+    def is_keyboard_shown(self) -> bool:
         """Attempts to detect whether a software keyboard is present
 
         Returns:
@@ -49,7 +54,7 @@ def is_keyboard_shown(self):
         """
         return self.execute(Command.IS_KEYBOARD_SHOWN)['value']
 
-    def keyevent(self, keycode, metastate=None):
+    def keyevent(self, keycode: int, metastate: Optional[int] = None) -> T:
         """Sends a keycode to the device.
 
         Android only.
@@ -70,7 +75,7 @@ def keyevent(self, keycode, metastate=None):
         self.execute(Command.KEY_EVENT, data)
         return self
 
-    def press_keycode(self, keycode, metastate=None, flags=None):
+    def press_keycode(self, keycode: int, metastate: Optional[int] = None, flags: Optional[int] = None) -> T:
         """Sends a keycode to the device.
 
         Android only. Possible keycodes can be found in http://developer.android.com/reference/android/view/KeyEvent.html.
@@ -93,7 +98,7 @@ def press_keycode(self, keycode, metastate=None, flags=None):
         self.execute(Command.PRESS_KEYCODE, data)
         return self
 
-    def long_press_keycode(self, keycode, metastate=None, flags=None):
+    def long_press_keycode(self, keycode: int, metastate: Optional[int] = None, flags: Optional[int] = None) -> T:
         """Sends a long press of keycode to the device.
 
         Android only. Possible keycodes can be found in http://developer.android.com/reference/android/view/KeyEvent.html.
@@ -118,7 +123,7 @@ def long_press_keycode(self, keycode, metastate=None, flags=None):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.HIDE_KEYBOARD] = \
             ('POST', '/session/$sessionId/appium/device/hide_keyboard')
         self.command_executor._commands[Command.IS_KEYBOARD_SHOWN] = \
diff --git a/appium/webdriver/extensions/location.py b/appium/webdriver/extensions/location.py
index 7dffcb0e..054cf44e 100644
--- a/appium/webdriver/extensions/location.py
+++ b/appium/webdriver/extensions/location.py
@@ -12,13 +12,17 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Dict, Optional, TypeVar, Union
+
 from selenium import webdriver
 
 from ..mobilecommand import MobileCommand as Command
 
+T = TypeVar('T', bound='Location')
+
 
 class Location(webdriver.Remote):
-    def toggle_location_services(self):
+    def toggle_location_services(self) -> T:
         """Toggle the location services on the device.
 
         Android only.
@@ -29,7 +33,10 @@ def toggle_location_services(self):
         self.execute(Command.TOGGLE_LOCATION_SERVICES, {})
         return self
 
-    def set_location(self, latitude, longitude, altitude=None):
+    def set_location(self,
+                     latitude: Union[float, str],
+                     longitude: Union[float, str],
+                     altitude: Union[float, str] = None) -> T:
         """Set the location of the device
 
         Args:
@@ -52,7 +59,7 @@ def set_location(self, latitude, longitude, altitude=None):
         return self
 
     @property
-    def location(self):
+    def location(self) -> Dict[str, float]:
         """Retrieves the current location
 
         Returns:
@@ -65,7 +72,7 @@ def location(self):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.TOGGLE_LOCATION_SERVICES] = \
             ('POST', '/session/$sessionId/appium/device/toggle_location_services')
         self.command_executor._commands[Command.GET_LOCATION] = \
diff --git a/appium/webdriver/extensions/log_event.py b/appium/webdriver/extensions/log_event.py
index 383664d6..b22c2416 100644
--- a/appium/webdriver/extensions/log_event.py
+++ b/appium/webdriver/extensions/log_event.py
@@ -12,14 +12,18 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Dict, List, TypeVar, Union
+
 from selenium import webdriver
 
 from ..mobilecommand import MobileCommand as Command
 
+T = TypeVar('T', bound='LogEvent')
+
 
 class LogEvent(webdriver.Remote):
 
-    def get_events(self, type=None):
+    def get_events(self, type: List[str] = None) -> Dict[str, Union[str, int]]:
         """ Retrieves events information from the current session
         (Since Appium 1.16.0)
 
@@ -35,14 +39,14 @@ def get_events(self, type=None):
                 commands: (`list` of `dict`) List of dictionaries containing the following entries
                     cmd: (str) The command name that has been sent to the appium server
                     startTime: (int) Received time
-                    endTime: (init) Response time
+                    endTime: (int) Response time
         """
         data = {}
         if type is not None:
             data['type'] = type
         return self.execute(Command.GET_EVENTS, data)['value']
 
-    def log_event(self, vendor, event):
+    def log_event(self, vendor: str, event: str) -> T:
         """Log a custom event on the Appium server.
         (Since Appium 1.16.0)
 
@@ -65,7 +69,7 @@ def log_event(self, vendor, event):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.GET_EVENTS] = \
             ('POST', '/session/$sessionId/appium/events')
         self.command_executor._commands[Command.LOG_EVENT] = \
diff --git a/appium/webdriver/extensions/remote_fs.py b/appium/webdriver/extensions/remote_fs.py
index 10fbff23..dd256a7a 100644
--- a/appium/webdriver/extensions/remote_fs.py
+++ b/appium/webdriver/extensions/remote_fs.py
@@ -13,50 +13,54 @@
 # limitations under the License.
 
 import base64
+from typing import Optional, TypeVar
 
 from selenium import webdriver
 from selenium.common.exceptions import InvalidArgumentException
 
 from ..mobilecommand import MobileCommand as Command
 
+T = TypeVar('T', bound='RemoteFS')
+
 
 class RemoteFS(webdriver.Remote):
-    def pull_file(self, path):
+    def pull_file(self, path: str) -> str:
         """Retrieves the file at `path`.
 
         Args:
             path (str): the path to the file on the device
 
         Returns:
-            bytes: The file's contents as base64.
+            str: The file's contents encoded as Base64.
         """
         data = {
             'path': path,
         }
         return self.execute(Command.PULL_FILE, data)['value']
 
-    def pull_folder(self, path):
+    def pull_folder(self, path: str) -> str:
         """Retrieves a folder at `path`.
 
         Args:
             path (str): the path to the folder on the device
 
         Returns:
-            bytes: The folder's contents zipped and encoded as Base64.
+            str: The folder's contents zipped and encoded as Base64.
         """
         data = {
             'path': path,
         }
         return self.execute(Command.PULL_FOLDER, data)['value']
 
-    def push_file(self, destination_path, base64data=None, source_path=None):
+    def push_file(self, destination_path: str,
+                  base64data: Optional[str] = None, source_path: Optional[str] = None) -> T:
         """Puts the data from the file at `source_path`, encoded as Base64, in the file specified as `path`.
 
         Specify either `base64data` or `source_path`, if both specified default to `source_path`
 
         Args:
             destination_path (str): the location on the device/simulator where the local file contents should be saved
-            base64data (:obj:`bytes`, optional): file contents, encoded as Base64, to be written to the file on the device/simulator
+            base64data (:obj:`str`, optional): file contents, encoded as Base64, to be written to the file on the device/simulator
             source_path (:obj:`str`, optional): local file path for the file to be loaded on device
 
         Returns:
@@ -68,11 +72,11 @@ def push_file(self, destination_path, base64data=None, source_path=None):
         if source_path is not None:
             try:
                 with open(source_path, 'rb') as f:
-                    data = f.read()
+                    file_data = f.read()
             except IOError:
                 message = 'source_path {} could not be found. Are you sure the file exists?'.format(source_path)
                 raise InvalidArgumentException(message)
-            base64data = base64.b64encode(data).decode('utf-8')
+            base64data = base64.b64encode(file_data).decode('utf-8')
 
         data = {
             'path': destination_path,
@@ -83,7 +87,7 @@ def push_file(self, destination_path, base64data=None, source_path=None):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.PULL_FILE] = \
             ('POST', '/session/$sessionId/appium/device/pull_file')
         self.command_executor._commands[Command.PULL_FOLDER] = \
diff --git a/appium/webdriver/extensions/screen_record.py b/appium/webdriver/extensions/screen_record.py
index 0b7f1bc7..8d2abbf0 100644
--- a/appium/webdriver/extensions/screen_record.py
+++ b/appium/webdriver/extensions/screen_record.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Any, Union
+
 from selenium import webdriver
 
 from ..mobilecommand import MobileCommand as Command
@@ -19,7 +21,7 @@
 
 class ScreenRecord(webdriver.Remote):
 
-    def start_recording_screen(self, **options):
+    def start_recording_screen(self, **options: Any) -> Union[bytes, str]:
         """Start asynchronous screen recording process.
 
         Keyword Args:
@@ -82,7 +84,7 @@ def start_recording_screen(self, **options):
             del options['password']
         return self.execute(Command.START_RECORDING_SCREEN, {'options': options})['value']
 
-    def stop_recording_screen(self, **options):
+    def stop_recording_screen(self, **options: Any) -> bytes:
         """Gather the output from the previously started screen recording to a media file.
 
         Keyword Args:
@@ -112,7 +114,7 @@ def stop_recording_screen(self, **options):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.START_RECORDING_SCREEN] = \
             ('POST', '/session/$sessionId/appium/start_recording_screen')
         self.command_executor._commands[Command.STOP_RECORDING_SCREEN] = \
diff --git a/appium/webdriver/extensions/search_context/android.py b/appium/webdriver/extensions/search_context/android.py
index 7c6f127a..4197eb99 100644
--- a/appium/webdriver/extensions/search_context/android.py
+++ b/appium/webdriver/extensions/search_context/android.py
@@ -15,16 +15,21 @@
 # pylint: disable=abstract-method
 
 import json
+from typing import TYPE_CHECKING, List, Optional
 
 from appium.webdriver.common.mobileby import MobileBy
 
 from .base_search_context import BaseSearchContext
 
+if TYPE_CHECKING:
+    from appium.webdriver.webelement import WebElement
+
 
 class AndroidSearchContext(BaseSearchContext):
     """Define search context for Android"""
 
-    def find_element_by_android_data_matcher(self, name=None, args=None, className=None):
+    def find_element_by_android_data_matcher(
+            self, name: Optional[str] = None, args: Optional[str] = None, className: Optional[str] = None) -> 'WebElement':
         """Finds element by [onData](https://medium.com/androiddevelopers/adapterviews-and-espresso-f4172aa853cf) in Android
 
         It works with [Espresso Driver](https://github.com/appium/appium-espresso-driver).
@@ -56,7 +61,8 @@ def find_element_by_android_data_matcher(self, name=None, args=None, className=N
             value=self._build_data_matcher(name=name, args=args, className=className)
         )
 
-    def find_elements_by_android_data_matcher(self, name=None, args=None, className=None):
+    def find_elements_by_android_data_matcher(
+            self, name: Optional[str] = None, args: Optional[str] = None, className: Optional[str] = None) -> List['WebElement']:
         """Finds elements by [onData](https://medium.com/androiddevelopers/adapterviews-and-espresso-f4172aa853cf) in Android
         It works with [Espresso Driver](https://github.com/appium/appium-espresso-driver).
 
@@ -83,7 +89,8 @@ def find_elements_by_android_data_matcher(self, name=None, args=None, className=
             value=self._build_data_matcher(name=name, args=args, className=className)
         )
 
-    def _build_data_matcher(self, name=None, args=None, className=None):
+    def _build_data_matcher(self, name: Optional[str] = None, args: Optional[str]
+                            = None, className: Optional[str] = None) -> str:
         result = {}
 
         for key, value in {'name': name, 'args': args, 'class': className}.items():
@@ -92,7 +99,7 @@ def _build_data_matcher(self, name=None, args=None, className=None):
 
         return json.dumps(result)
 
-    def find_element_by_android_uiautomator(self, uia_string):
+    def find_element_by_android_uiautomator(self, uia_string: str) -> 'WebElement':
         """Finds element by uiautomator in Android.
 
         Args:
@@ -108,7 +115,7 @@ def find_element_by_android_uiautomator(self, uia_string):
         """
         return self.find_element(by=MobileBy.ANDROID_UIAUTOMATOR, value=uia_string)
 
-    def find_elements_by_android_uiautomator(self, uia_string):
+    def find_elements_by_android_uiautomator(self, uia_string: str) -> List['WebElement']:
         """Finds elements by uiautomator in Android.
 
         Args:
@@ -124,7 +131,7 @@ def find_elements_by_android_uiautomator(self, uia_string):
         """
         return self.find_elements(by=MobileBy.ANDROID_UIAUTOMATOR, value=uia_string)
 
-    def find_element_by_android_viewtag(self, tag):
+    def find_element_by_android_viewtag(self, tag: str) -> 'WebElement':
         """Finds element by [View#tags](https://developer.android.com/reference/android/view/View#tags) in Android.
 
         It works with [Espresso Driver](https://github.com/appium/appium-espresso-driver).
@@ -142,7 +149,7 @@ def find_element_by_android_viewtag(self, tag):
         """
         return self.find_element(by=MobileBy.ANDROID_VIEWTAG, value=tag)
 
-    def find_elements_by_android_viewtag(self, tag):
+    def find_elements_by_android_viewtag(self, tag: str) -> List['WebElement']:
         """Finds element by [View#tags](https://developer.android.com/reference/android/view/View#tags) in Android.
 
         It works with [Espresso Driver](https://github.com/appium/appium-espresso-driver).
diff --git a/appium/webdriver/extensions/search_context/base_search_context.py b/appium/webdriver/extensions/search_context/base_search_context.py
index 500a6e3a..404aa62a 100644
--- a/appium/webdriver/extensions/search_context/base_search_context.py
+++ b/appium/webdriver/extensions/search_context/base_search_context.py
@@ -14,12 +14,17 @@
 
 # pylint: disable=abstract-method
 
+from typing import TYPE_CHECKING, Dict, List, Optional, Union
+
+if TYPE_CHECKING:
+    from appium.webdriver.webelement import WebElement
+
 
 class BaseSearchContext(object):
     """Used by each search context. Dummy find_element/s are for preventing pylint error"""
 
-    def find_element(self, by=None, value=None):
+    def find_element(self, by: str, value: Union[str, Dict] = None) -> 'WebElement':
         raise NotImplementedError
 
-    def find_elements(self, by=None, value=None):
+    def find_elements(self, by: str, value: Union[str, Dict] = None) -> List['WebElement']:
         raise NotImplementedError
diff --git a/appium/webdriver/extensions/search_context/custom.py b/appium/webdriver/extensions/search_context/custom.py
index dabcc6fd..a790016b 100644
--- a/appium/webdriver/extensions/search_context/custom.py
+++ b/appium/webdriver/extensions/search_context/custom.py
@@ -14,15 +14,20 @@
 
 # pylint: disable=abstract-method
 
+from typing import TYPE_CHECKING, List
+
 from appium.webdriver.common.mobileby import MobileBy
 
 from .base_search_context import BaseSearchContext
 
+if TYPE_CHECKING:
+    from appium.webdriver.webelement import WebElement
+
 
 class CustomSearchContext(BaseSearchContext):
     """Define search context for custom plugin"""
 
-    def find_element_by_custom(self, selector):
+    def find_element_by_custom(self, selector: str) -> 'WebElement':
         """Finds an element in conjunction with a custom element finding plugin
 
         Args:
@@ -42,7 +47,7 @@ def find_element_by_custom(self, selector):
         """
         return self.find_element(by=MobileBy.CUSTOM, value=selector)
 
-    def find_elements_by_custom(self, selector):
+    def find_elements_by_custom(self, selector: str) -> List['WebElement']:
         """Finds elements in conjunction with a custom element finding plugin
 
         Args:
diff --git a/appium/webdriver/extensions/search_context/ios.py b/appium/webdriver/extensions/search_context/ios.py
index ad42ce91..3066ad9e 100644
--- a/appium/webdriver/extensions/search_context/ios.py
+++ b/appium/webdriver/extensions/search_context/ios.py
@@ -14,15 +14,20 @@
 
 # pylint: disable=abstract-method
 
+from typing import TYPE_CHECKING, List
+
 from appium.webdriver.common.mobileby import MobileBy
 
 from .base_search_context import BaseSearchContext
 
+if TYPE_CHECKING:
+    from appium.webdriver.webelement import WebElement
+
 
 class iOSSearchContext(BaseSearchContext):
     """Define search context for iOS"""
 
-    def find_element_by_ios_uiautomation(self, uia_string):
+    def find_element_by_ios_uiautomation(self, uia_string: str) -> 'WebElement':
         """Finds an element by uiautomation in iOS.
 
         Args:
@@ -39,7 +44,7 @@ def find_element_by_ios_uiautomation(self, uia_string):
         """
         return self.find_element(by=MobileBy.IOS_UIAUTOMATION, value=uia_string)
 
-    def find_elements_by_ios_uiautomation(self, uia_string):
+    def find_elements_by_ios_uiautomation(self, uia_string: str) -> List['WebElement']:
         """Finds elements by uiautomation in iOS.
 
         Args:
@@ -55,7 +60,7 @@ def find_elements_by_ios_uiautomation(self, uia_string):
         """
         return self.find_elements(by=MobileBy.IOS_UIAUTOMATION, value=uia_string)
 
-    def find_element_by_ios_predicate(self, predicate_string):
+    def find_element_by_ios_predicate(self, predicate_string: str) -> 'WebElement':
         """Find an element by ios predicate string.
 
         Args:
@@ -71,7 +76,7 @@ def find_element_by_ios_predicate(self, predicate_string):
         """
         return self.find_element(by=MobileBy.IOS_PREDICATE, value=predicate_string)
 
-    def find_elements_by_ios_predicate(self, predicate_string):
+    def find_elements_by_ios_predicate(self, predicate_string: str) -> List['WebElement']:
         """Finds elements by ios predicate string.
 
         Args:
@@ -87,7 +92,7 @@ def find_elements_by_ios_predicate(self, predicate_string):
         """
         return self.find_elements(by=MobileBy.IOS_PREDICATE, value=predicate_string)
 
-    def find_element_by_ios_class_chain(self, class_chain_string):
+    def find_element_by_ios_class_chain(self, class_chain_string: str) -> 'WebElement':
         """Find an element by ios class chain string.
 
         Args:
@@ -103,7 +108,7 @@ def find_element_by_ios_class_chain(self, class_chain_string):
         """
         return self.find_element(by=MobileBy.IOS_CLASS_CHAIN, value=class_chain_string)
 
-    def find_elements_by_ios_class_chain(self, class_chain_string):
+    def find_elements_by_ios_class_chain(self, class_chain_string: str) -> List['WebElement']:
         """Finds elements by ios class chain string.
 
         Args:
diff --git a/appium/webdriver/extensions/search_context/mobile.py b/appium/webdriver/extensions/search_context/mobile.py
index c9d68632..a58f4d23 100644
--- a/appium/webdriver/extensions/search_context/mobile.py
+++ b/appium/webdriver/extensions/search_context/mobile.py
@@ -15,16 +15,20 @@
 # pylint: disable=abstract-method
 
 import base64
+from typing import TYPE_CHECKING, List
 
 from appium.webdriver.common.mobileby import MobileBy
 
 from .base_search_context import BaseSearchContext
 
+if TYPE_CHECKING:
+    from appium.webdriver.webelement import WebElement
+
 
 class MobileSearchContext(BaseSearchContext):
     """Define search context for Mobile(Android, iOS)"""
 
-    def find_element_by_accessibility_id(self, accessibility_id):
+    def find_element_by_accessibility_id(self, accessibility_id: str) -> 'WebElement':
         """Finds an element by accessibility id.
 
         Args:
@@ -42,7 +46,7 @@ def find_element_by_accessibility_id(self, accessibility_id):
         """
         return self.find_element(by=MobileBy.ACCESSIBILITY_ID, value=accessibility_id)
 
-    def find_elements_by_accessibility_id(self, accessibility_id):
+    def find_elements_by_accessibility_id(self, accessibility_id: str) -> List['WebElement']:
         """Finds elements by accessibility id.
 
         Args:
@@ -59,7 +63,7 @@ def find_elements_by_accessibility_id(self, accessibility_id):
         """
         return self.find_elements(by=MobileBy.ACCESSIBILITY_ID, value=accessibility_id)
 
-    def find_element_by_image(self, img_path):
+    def find_element_by_image(self, img_path: str) -> 'WebElement':
         """Finds a portion of a screenshot by an image.
 
         Uses driver.find_image_occurrence under the hood.
@@ -77,7 +81,7 @@ def find_element_by_image(self, img_path):
 
         return self.find_element(by=MobileBy.IMAGE, value=b64_data)
 
-    def find_elements_by_image(self, img_path):
+    def find_elements_by_image(self, img_path: str) -> List['WebElement']:
         """Finds a portion of a screenshot by an image.
 
         Uses driver.find_image_occurrence under the hood. Note that this will
diff --git a/appium/webdriver/extensions/search_context/windows.py b/appium/webdriver/extensions/search_context/windows.py
index 66ca23a2..692aebce 100644
--- a/appium/webdriver/extensions/search_context/windows.py
+++ b/appium/webdriver/extensions/search_context/windows.py
@@ -14,15 +14,20 @@
 
 # pylint: disable=abstract-method
 
+from typing import TYPE_CHECKING, List
+
 from appium.webdriver.common.mobileby import MobileBy
 
 from .base_search_context import BaseSearchContext
 
+if TYPE_CHECKING:
+    from appium.webdriver.webelement import WebElement
+
 
 class WindowsSearchContext(BaseSearchContext):
     """Define search context for Windows"""
 
-    def find_element_by_windows_uiautomation(self, win_uiautomation):
+    def find_element_by_windows_uiautomation(self, win_uiautomation: str) -> 'WebElement':
         """Finds an element by windows uiautomation
 
         Args:
@@ -39,7 +44,7 @@ def find_element_by_windows_uiautomation(self, win_uiautomation):
         """
         return self.find_element(by=MobileBy.WINDOWS_UI_AUTOMATION, value=win_uiautomation)
 
-    def find_elements_by_windows_uiautomation(self, win_uiautomation):
+    def find_elements_by_windows_uiautomation(self, win_uiautomation: str) -> List['WebElement']:
         """Finds elements by windows uiautomation
 
         Args:
diff --git a/appium/webdriver/extensions/session.py b/appium/webdriver/extensions/session.py
index 64d49370..a8c097a6 100644
--- a/appium/webdriver/extensions/session.py
+++ b/appium/webdriver/extensions/session.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Any, Dict, List
+
 from selenium import webdriver
 
 from appium.common.logger import logger
@@ -21,7 +23,7 @@
 
 class Session(webdriver.Remote):
     @property
-    def session(self):
+    def session(self) -> Dict[str, Any]:
         """ Retrieves session information from the current session
 
         Usage:
@@ -33,19 +35,19 @@ def session(self):
         return self.execute(Command.GET_SESSION)['value']
 
     @property
-    def all_sessions(self):
+    def all_sessions(self) -> List[Dict[str, Any]]:
         """ Retrieves all sessions that are open
 
         Usage:
             sessions = driver.all_sessions
 
         Returns:
-            `dict`: containing all open sessions
+            :obj:`list` of :obj:`dict`: containing all open sessions
         """
         return self.execute(Command.GET_ALL_SESSIONS)['value']
 
     @property
-    def events(self):
+    def events(self) -> Dict:
         """ Retrieves events information from the current session
 
         Usage:
@@ -63,7 +65,7 @@ def events(self):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.GET_SESSION] = \
             ('GET', '/session/$sessionId')
         self.command_executor._commands[Command.GET_ALL_SESSIONS] = \
diff --git a/appium/webdriver/extensions/settings.py b/appium/webdriver/extensions/settings.py
index 2a0f4235..b5514621 100644
--- a/appium/webdriver/extensions/settings.py
+++ b/appium/webdriver/extensions/settings.py
@@ -12,13 +12,17 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Any, Dict, TypeVar
+
 from selenium import webdriver
 
 from ..mobilecommand import MobileCommand as Command
 
+T = TypeVar('T', bound='Settings')
+
 
 class Settings(webdriver.Remote):
-    def get_settings(self):
+    def get_settings(self) -> Dict[str, Any]:
         """Returns the appium server Settings for the current session.
 
         Do not get Settings confused with Desired Capabilities, they are
@@ -29,7 +33,7 @@ def get_settings(self):
         """
         return self.execute(Command.GET_SETTINGS, {})['value']
 
-    def update_settings(self, settings):
+    def update_settings(self, settings: Dict[str, Any]) -> T:
         """Set settings for the current session.
 
         For more on settings, see: https://github.com/appium/appium/blob/master/docs/en/advanced-concepts/settings.md
@@ -44,7 +48,7 @@ def update_settings(self, settings):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         self.command_executor._commands[Command.GET_SETTINGS] = \
             ('GET', '/session/$sessionId/appium/settings')
         self.command_executor._commands[Command.UPDATE_SETTINGS] = \
diff --git a/appium/webdriver/switch_to.py b/appium/webdriver/switch_to.py
index d496b7a3..e0266510 100644
--- a/appium/webdriver/switch_to.py
+++ b/appium/webdriver/switch_to.py
@@ -12,13 +12,17 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import TypeVar
+
 from selenium.webdriver.remote.switch_to import SwitchTo
 
 from .mobilecommand import MobileCommand
 
+T = TypeVar('T', bound='MobileSwitchTo')
+
 
 class MobileSwitchTo(SwitchTo):
-    def context(self, context_name):
+    def context(self, context_name: str) -> T:
         """Sets the context for the current session.
 
         Args:
@@ -28,3 +32,4 @@ def context(self, context_name):
             driver.switch_to.context('WEBVIEW_1')
         """
         self._driver.execute(MobileCommand.SWITCH_TO_CONTEXT, {'name': context_name})
+        return self
diff --git a/appium/webdriver/webdriver.py b/appium/webdriver/webdriver.py
index 03e7e3fd..13e9619f 100644
--- a/appium/webdriver/webdriver.py
+++ b/appium/webdriver/webdriver.py
@@ -15,6 +15,7 @@
 # pylint: disable=too-many-lines,too-many-public-methods,too-many-statements,no-self-use
 
 import copy
+from typing import Any, Dict, List, Optional, TypeVar, Union
 
 from selenium.common.exceptions import InvalidArgumentException
 from selenium.webdriver.common.by import By
@@ -84,7 +85,7 @@
 # Add appium prefix for the non-W3C capabilities
 
 
-def _make_w3c_caps(caps):
+def _make_w3c_caps(caps: Dict) -> Dict[str, List[Dict[str, Any]]]:
     appium_prefix = 'appium:'
 
     caps = copy.deepcopy(caps)
@@ -111,6 +112,9 @@ def _make_w3c_caps(caps):
     return {'firstMatch': [first_match]}
 
 
+T = TypeVar('T', bound='WebDriver')
+
+
 class WebDriver(
     AppiumSearchContext,
     ActionHelpers,
@@ -141,8 +145,8 @@ class WebDriver(
     SystemBars
 ):
 
-    def __init__(self, command_executor='http://127.0.0.1:4444/wd/hub',
-                 desired_capabilities=None, browser_profile=None, proxy=None, keep_alive=True, direct_connection=False):
+    def __init__(self, command_executor: str = 'http://127.0.0.1:4444/wd/hub',
+                 desired_capabilities: Optional[Dict] = None, browser_profile: str = None, proxy: str = None, keep_alive: bool = True, direct_connection: bool = False):
 
         super(WebDriver, self).__init__(
             AppiumConnection(command_executor, keep_alive=keep_alive),
@@ -171,7 +175,7 @@ def __init__(self, command_executor='http://127.0.0.1:4444/wd/hub',
         By.IMAGE = MobileBy.IMAGE
         By.CUSTOM = MobileBy.CUSTOM
 
-    def _update_command_executor(self, keep_alive):
+    def _update_command_executor(self, keep_alive: bool) -> None:
         """Update command executor following directConnect feature"""
         direct_protocol = 'directConnectProtocol'
         direct_host = 'directConnectHost'
@@ -201,7 +205,7 @@ def _update_command_executor(self, keep_alive):
         self.command_executor = RemoteConnection(executor, keep_alive=keep_alive)
         self._addCommands()
 
-    def start_session(self, capabilities, browser_profile=None):
+    def start_session(self, capabilities: Dict, browser_profile: Optional[str] = None) -> None:
         """Creates a new session with the desired capabilities.
 
         Override for Appium
@@ -218,9 +222,11 @@ def start_session(self, capabilities, browser_profile=None):
             raise InvalidArgumentException('Capabilities must be a dictionary')
         if browser_profile:
             if 'moz:firefoxOptions' in capabilities:
-                capabilities['moz:firefoxOptions']['profile'] = browser_profile.encoded
+                # encoded is defined in selenium's original codes
+                capabilities['moz:firefoxOptions']['profile'] = browser_profile.encoded  # type: ignore
             else:
-                capabilities.update({'firefox_profile': browser_profile.encoded})
+                # encoded is defined in selenium's original codes
+                capabilities.update({'firefox_profile': browser_profile.encoded})  # type: ignore
 
         parameters = self._merge_capabilities(capabilities)
 
@@ -239,7 +245,7 @@ def start_session(self, capabilities, browser_profile=None):
         self.w3c = response.get('status') is None
         self.command_executor.w3c = self.w3c
 
-    def _merge_capabilities(self, capabilities):
+    def _merge_capabilities(self, capabilities: Dict) -> Dict[str, Any]:
         """Manage capabilities whether W3C format or MJSONWP format
         """
         if _FORCE_MJSONWP in capabilities:
@@ -252,7 +258,7 @@ def _merge_capabilities(self, capabilities):
         w3c_caps = _make_w3c_caps(capabilities)
         return {'capabilities': w3c_caps, 'desiredCapabilities': capabilities}
 
-    def find_element(self, by=By.ID, value=None):
+    def find_element(self, by: str = By.ID, value: Union[str, Dict] = None) -> MobileWebElement:
         """'Private' method used by the find_element_by_* methods.
 
         Override for Appium
@@ -283,7 +289,8 @@ def find_element(self, by=By.ID, value=None):
             'using': by,
             'value': value})['value']
 
-    def find_elements(self, by=By.ID, value=None):
+    def find_elements(self, by: str = By.ID, value: Union[str, Dict]
+                      = None) -> Union[List[MobileWebElement], List]:
         """'Private' method used by the find_elements_by_* methods.
 
         Override for Appium
@@ -317,7 +324,7 @@ def find_elements(self, by=By.ID, value=None):
             'using': by,
             'value': value})['value'] or []
 
-    def create_web_element(self, element_id, w3c=False):
+    def create_web_element(self, element_id: int, w3c: bool = False) -> MobileWebElement:
         """Creates a web element with the specified element_id.
 
         Overrides method in Selenium WebDriver in order to always give them
@@ -332,7 +339,7 @@ def create_web_element(self, element_id, w3c=False):
         """
         return MobileWebElement(self, element_id, w3c)
 
-    def set_value(self, element, value):
+    def set_value(self, element: MobileWebElement, value: str) -> T:
         """Set the value on an element in the application.
 
         Args:
@@ -351,7 +358,7 @@ def set_value(self, element, value):
 
     # pylint: disable=protected-access
 
-    def _addCommands(self):
+    def _addCommands(self) -> None:
         # call the overridden command binders from all mixin classes except for
         # appium.webdriver.webdriver.WebDriver and its sub-classes
         # https://github.com/appium/python-client/issues/342
diff --git a/appium/webdriver/webelement.py b/appium/webdriver/webelement.py
index bf8efc5b..ce9e8f80 100644
--- a/appium/webdriver/webelement.py
+++ b/appium/webdriver/webelement.py
@@ -12,21 +12,19 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Dict, List, Optional, TypeVar, Union
+
 from selenium.webdriver.common.by import By
 from selenium.webdriver.remote.command import Command as RemoteCommand
 
 from .extensions.search_context import AppiumWebElementSearchContext
 from .mobilecommand import MobileCommand as Command
 
-# Python 3 imports
-try:
-    str = basestring
-except NameError:
-    pass
+T = TypeVar('T', bound='WebElement')
 
 
 class WebElement(AppiumWebElementSearchContext):
-    def get_attribute(self, name):
+    def get_attribute(self, name: str) -> Optional[str]:
         """Gets the given attribute or property of the element.
 
         Override for Appium
@@ -58,22 +56,23 @@ def get_attribute(self, name):
         if attributeValue is None:
             return None
 
+        # Convert to str along to the spec
         if not isinstance(attributeValue, str):
-            attributeValue = unicode(attributeValue)
+            attributeValue = str(attributeValue)
 
         if name != 'value' and attributeValue.lower() in ('true', 'false'):
             return attributeValue.lower()
 
         return attributeValue
 
-    def is_displayed(self):
+    def is_displayed(self) -> bool:
         """Whether the element is visible to a user.
 
         Override for Appium
         """
         return self._execute(RemoteCommand.IS_ELEMENT_DISPLAYED)['value']
 
-    def find_element(self, by=By.ID, value=None):
+    def find_element(self, by: str = By.ID, value: Union[str, Dict] = None) -> T:
         """Find an element given a By strategy and locator
 
         Override for Appium
@@ -107,7 +106,7 @@ def find_element(self, by=By.ID, value=None):
         return self._execute(RemoteCommand.FIND_CHILD_ELEMENT,
                              {"using": by, "value": value})['value']
 
-    def find_elements(self, by=By.ID, value=None):
+    def find_elements(self, by: str = By.ID, value: Union[str, Dict] = None) -> List[T]:
         """Find elements given a By strategy and locator
 
         Override for Appium
@@ -141,7 +140,7 @@ def find_elements(self, by=By.ID, value=None):
         return self._execute(RemoteCommand.FIND_CHILD_ELEMENTS,
                              {"using": by, "value": value})['value']
 
-    def clear(self):
+    def clear(self) -> T:
         """Clears text.
 
         Override for Appium
@@ -153,7 +152,7 @@ def clear(self):
         self._execute(Command.CLEAR, data)
         return self
 
-    def set_text(self, keys=''):
+    def set_text(self, keys: str = '') -> T:
         """Sends text to the element.
 
         Previous text is removed.
@@ -176,7 +175,7 @@ def set_text(self, keys=''):
         return self
 
     @property
-    def location_in_view(self):
+    def location_in_view(self) -> Dict[str, int]:
         """Gets the location of an element relative to the view.
 
         Usage:
@@ -189,7 +188,7 @@ def location_in_view(self):
         """
         return self._execute(Command.LOCATION_IN_VIEW)['value']
 
-    def set_value(self, value):
+    def set_value(self, value: str) -> T:
         """Set the value on this element in the application
 
         Args:
diff --git a/ci.sh b/ci.sh
index 0fb53862..a0b1d8fc 100755
--- a/ci.sh
+++ b/ci.sh
@@ -34,4 +34,11 @@ if [[ $? -ne 0 ]] ; then
   EXIT_STATUS=1
 fi
 
+(
+  python -m mypy appium
+)
+if [[ $? -ne 0 ]] ; then
+  EXIT_STATUS=1
+fi
+
 exit $EXIT_STATUS
diff --git a/mypy.ini b/mypy.ini
new file mode 100644
index 00000000..42606f97
--- /dev/null
+++ b/mypy.ini
@@ -0,0 +1,9 @@
+[mypy]
+check_untyped_defs = True
+disallow_untyped_calls = True
+disallow_untyped_defs = True
+follow_imports = skip
+ignore_missing_imports = True
+strict_optional = True
+warn_redundant_casts = True
+warn_unused_ignores = True
diff --git a/test/functional/android/remote_fs_tests.py b/test/functional/android/remote_fs_tests.py
index fefe0839..1a7a0092 100644
--- a/test/functional/android/remote_fs_tests.py
+++ b/test/functional/android/remote_fs_tests.py
@@ -19,15 +19,13 @@
 from io import BytesIO
 from zipfile import ZipFile
 
-from appium.common.helper import appium_bytes
-
 from .helper.test_helper import BaseTestCase
 
 
 class RemoteFsTests(BaseTestCase):
     def test_push_pull_file(self):
         dest_path = '/data/local/tmp/test_push_file.txt'
-        data = appium_bytes('This is the contents of the file to push to the device.', 'utf-8')
+        data = bytes('This is the contents of the file to push to the device.', 'utf-8')
 
         self.driver.push_file(dest_path, base64.b64encode(data).decode('utf-8'))
         data_ret = base64.b64decode(self.driver.pull_file(dest_path))
@@ -35,7 +33,7 @@ def test_push_pull_file(self):
         self.assertEqual(data, data_ret)
 
     def test_pull_folder(self):
-        data = appium_bytes('random string data {}'.format(random.randint(0, 1000)), 'utf-8')
+        data = bytes('random string data {}'.format(random.randint(0, 1000)), 'utf-8')
         dest_dir = '/data/local/tmp/'
 
         for filename in ['1.txt', '2.txt']:
diff --git a/test/unit/webdriver/device/clipboard_test.py b/test/unit/webdriver/device/clipboard_test.py
index 22c80dbe..01176029 100644
--- a/test/unit/webdriver/device/clipboard_test.py
+++ b/test/unit/webdriver/device/clipboard_test.py
@@ -14,7 +14,6 @@
 
 import httpretty
 
-from appium.common.helper import appium_bytes
 from appium.webdriver.clipboard_content_type import ClipboardContentType
 from test.unit.helper.test_helper import (
     android_w3c_driver,
@@ -34,7 +33,7 @@ def test_set_clipboard_with_url(self):
             appium_command('/session/1234567890/appium/device/set_clipboard'),
             body='{"value": ""}'
         )
-        driver.set_clipboard(appium_bytes(str('http://appium.io/'), 'UTF-8'),
+        driver.set_clipboard(bytes(str('http://appium.io/'), 'UTF-8'),
                              ClipboardContentType.URL, 'label for android')
 
         d = get_httpretty_request_body(httpretty.last_request())
diff --git a/test/unit/webdriver/device/remote_fs_test.py b/test/unit/webdriver/device/remote_fs_test.py
index 0855b936..dace0ffc 100644
--- a/test/unit/webdriver/device/remote_fs_test.py
+++ b/test/unit/webdriver/device/remote_fs_test.py
@@ -18,7 +18,6 @@
 import pytest
 from selenium.common.exceptions import InvalidArgumentException
 
-from appium.common.helper import appium_bytes
 from appium.webdriver.webdriver import WebDriver
 from test.unit.helper.test_helper import (
     android_w3c_driver,
@@ -37,7 +36,7 @@ def test_push_file(self):
             appium_command('/session/1234567890/appium/device/push_file'),
         )
         dest_path = '/path/to/file.txt'
-        data = base64.b64encode(appium_bytes('HelloWorld', 'utf-8')).decode('utf-8')
+        data = base64.b64encode(bytes('HelloWorld', 'utf-8')).decode('utf-8')
 
         assert isinstance(driver.push_file(dest_path, data), WebDriver)
 
@@ -80,7 +79,7 @@ def test_pull_file(self):
         )
         dest_path = '/path/to/file.txt'
 
-        assert driver.pull_file(dest_path) == str(base64.b64encode(appium_bytes('HelloWorld', 'utf-8')).decode('utf-8'))
+        assert driver.pull_file(dest_path) == str(base64.b64encode(bytes('HelloWorld', 'utf-8')).decode('utf-8'))
 
         d = get_httpretty_request_body(httpretty.last_request())
         assert d['path'] == dest_path