diff --git a/.travis.yml b/.travis.yml
index 832f535..d150541 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -15,7 +15,14 @@
 # limitations under the License.
 
 language: python
-python: [ "2.7" ]
+matrix:
+  include:
+    - python: "2.7"
+      env: REQUIREMENTS=requirements-dev.txt VENV=python2.7
+    - python: "pypy"
+      env: REQUIREMENTS=requirements-dev.txt VENV=pypy
+    - python: "3.3"
+      env: REQUIREMENTS=requirements3-dev.txt VENV=python3.3
 
 before_install: |
   # needed for the UML container
@@ -37,5 +44,5 @@ before_install: |
   chmod +x tests.sh
   chmod +x run.sh
 
-install: pip install -r requirements-dev.txt
+install: pip install -r $REQUIREMENTS
 script: ./run.sh
diff --git a/dockerpty/io.py b/dockerpty/io.py
index dda53fb..06282b5 100644
--- a/dockerpty/io.py
+++ b/dockerpty/io.py
@@ -19,6 +19,7 @@
 import errno
 import struct
 import select as builtin_select
+import six
 
 
 def set_blocking(fd, blocking=True):
@@ -31,7 +32,7 @@ def set_blocking(fd, blocking=True):
     old_flag = fcntl.fcntl(fd, fcntl.F_GETFL)
 
     if blocking:
-        new_flag = old_flag &~ os.O_NONBLOCK
+        new_flag = old_flag & ~ os.O_NONBLOCK
     else:
         new_flag = old_flag | os.O_NONBLOCK
 
@@ -59,7 +60,8 @@ def select(read_streams, timeout=0):
         )[0]
     except builtin_select.error as e:
         # POSIX signals interrupt select()
-        if e[0] == errno.EINTR:
+        no = e.errno if six.PY3 else e[0]
+        if no == errno.EINTR:
             return []
         else:
             raise e
@@ -73,7 +75,6 @@ class Stream(object):
     add consistency to the reading of sockets and files alike.
     """
 
-
     """
     Recoverable IO/OS Errors.
     """
@@ -83,7 +84,6 @@ class Stream(object):
         errno.EWOULDBLOCK,
     ]
 
-
     def __init__(self, fd):
         """
         Initialize the Stream for the file descriptor `fd`.
@@ -92,7 +92,6 @@ def __init__(self, fd):
         """
         self.fd = fd
 
-
     def fileno(self):
         """
         Return the fileno() of the file descriptor.
@@ -100,7 +99,6 @@ def fileno(self):
 
         return self.fd.fileno()
 
-
     def set_blocking(self, value):
         if hasattr(self.fd, 'setblocking'):
             self.fd.setblocking(value)
@@ -108,7 +106,6 @@ def set_blocking(self, value):
         else:
             return set_blocking(self.fd, value)
 
-
     def read(self, n=4096):
         """
         Return `n` bytes of data from the Stream, or None at end of stream.
@@ -122,7 +119,6 @@ def read(self, n=4096):
             if e.errno not in Stream.ERRNO_RECOVERABLE:
                 raise e
 
-
     def write(self, data):
         """
         Write `data` to the Stream.
@@ -170,7 +166,6 @@ def __init__(self, stream):
         self.stream = stream
         self.remain = 0
 
-
     def fileno(self):
         """
         Returns the fileno() of the underlying Stream.
@@ -180,11 +175,9 @@ def fileno(self):
 
         return self.stream.fileno()
 
-
     def set_blocking(self, value):
         return self.stream.set_blocking(value)
 
-
     def read(self, n=4096):
         """
         Read up to `n` bytes of data from the Stream, after demuxing.
@@ -201,16 +194,15 @@ def read(self, n=4096):
         if size <= 0:
             return
         else:
-            data = ''
+            data = six.binary_type()
             while len(data) < size:
                 nxt = self.stream.read(size - len(data))
                 if not nxt:
                     # the stream has closed, return what data we got
                     return data
-                data = "{0}{1}".format(data, nxt)
+                data = data + nxt
             return data
 
-
     def write(self, data):
         """
         Delegates the the underlying Stream.
@@ -218,7 +210,6 @@ def write(self, data):
 
         return self.stream.write(data)
 
-
     def _next_packet_size(self, n=0):
         size = 0
 
@@ -226,13 +217,13 @@ def _next_packet_size(self, n=0):
             size = min(n, self.remain)
             self.remain -= size
         else:
-            data = ''
+            data = six.binary_type()
             while len(data) < 8:
                 nxt = self.stream.read(8 - len(data))
                 if not nxt:
                     # The stream has closed, there's nothing more to read
                     return 0
-                data = "{0}{1}".format(data, nxt)
+                data = data + nxt
 
             if data is None:
                 return 0
@@ -270,7 +261,6 @@ def __init__(self, from_stream, to_stream):
         self.from_stream = from_stream
         self.to_stream = to_stream
 
-
     def fileno(self):
         """
         Returns the `fileno()` of the reader end of the Pump.
@@ -280,11 +270,9 @@ def fileno(self):
 
         return self.from_stream.fileno()
 
-
     def set_blocking(self, value):
         return self.from_stream.set_blocking(value)
 
-
     def flush(self, n=4096):
         """
         Flush `n` bytes of data from the reader Stream to the writer Stream.
diff --git a/features/steps/step_definitions.py b/features/steps/step_definitions.py
index b630af0..0c34ba8 100644
--- a/features/steps/step_definitions.py
+++ b/features/steps/step_definitions.py
@@ -14,7 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from behave import *
+from behave import then, given, when
 from expects import expect, equal, be_true, be_false
 import tests.util as util
 
@@ -23,8 +23,8 @@
 import sys
 import os
 import signal
-import errno
 import time
+import six
 
 
 @given('I am using a TTY')
@@ -97,6 +97,7 @@ def step_impl(ctx):
         )
         ctx.pid = pid
         util.wait(ctx.pty, timeout=5)
+    time.sleep(1) # give the terminal some time to print prompt
 
 
 @when('I resize the terminal to {rows} x {cols}')
@@ -113,22 +114,21 @@ def step_impl(ctx, rows, cols):
 
 @when('I type "{text}"')
 def step_impl(ctx, text):
-    util.write(ctx.pty, text)
-
+    util.write(ctx.pty, text.encode())
 
 @when('I press {key}')
 def step_impl(ctx, key):
     mappings = {
-        "enter": "\x0a",
-        "up":    "\x1b[A",
-        "down":  "\x1b[B",
-        "right": "\x1b[C",
-        "left":  "\x1b[D",
-        "esc":   "\x1b",
-        "c-c":   "\x03",
-        "c-d":   "\x04",
-        "c-p":   "\x10",
-        "c-q":   "\x11",
+        "enter": b"\x0a",
+        "up":    b"\x1b[A",
+        "down":  b"\x1b[B",
+        "right": b"\x1b[C",
+        "left":  b"\x1b[D",
+        "esc":   b"\x1b",
+        "c-c":   b"\x03",
+        "c-d":   b"\x04",
+        "c-p":   b"\x10",
+        "c-q":   b"\x11",
     }
     util.write(ctx.pty, mappings[key.lower()])
 
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 78fe60c..c0ea3ed 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -2,3 +2,4 @@ docker-py>=0.3.2
 pytest>=2.5.2
 behave>=1.2.4
 expects>=0.4
+six>=1.3.0
diff --git a/requirements.txt b/requirements.txt
new file mode 100644
index 0000000..6913a59
--- /dev/null
+++ b/requirements.txt
@@ -0,0 +1 @@
+six>=1.3.0
diff --git a/requirements3-dev.txt b/requirements3-dev.txt
new file mode 100644
index 0000000..fdd3511
--- /dev/null
+++ b/requirements3-dev.txt
@@ -0,0 +1,5 @@
+docker-py>=0.7.1
+pytest>=2.5.2
+behave>=1.2.4
+expects>=0.4
+six>=1.3.0
diff --git a/run.sh b/run.sh
index 6bb0255..ee1b892 100644
--- a/run.sh
+++ b/run.sh
@@ -6,7 +6,7 @@ echo 1 > /tmp/build.status
 # run the build inside UML kernel
 ./linux quiet mem=2G rootfstype=hostfs rw \
     eth0=slirp,,/usr/bin/slirp-fullbolt \
-    init=$(pwd)/tests.sh WORKDIR=$(pwd) HOME=$HOME
+    init=$(pwd)/tests.sh WORKDIR=$(pwd) VENV=$VENV HOME=$HOME
 
 # grab the build result and use it
 exit $(cat /tmp/build.status)
diff --git a/setup.py b/setup.py
index 2b7165d..03dcbd1 100644
--- a/setup.py
+++ b/setup.py
@@ -17,9 +17,11 @@
 from setuptools import setup
 import os
 
+
 def fopen(filename):
     return open(os.path.join(os.path.dirname(__file__), filename))
 
+
 def read(filename):
     return fopen(filename).read()
 
@@ -31,6 +33,7 @@ def read(filename):
     url='https://github.com/d11wtq/dockerpty',
     author='Chris Corbyn',
     author_email='chris@w3style.co.uk',
+    install_requires=['six >= 1.3.0'],
     license='Apache 2.0',
     keywords='docker, tty, pty, terminal',
     packages=['dockerpty'],
diff --git a/tests.sh b/tests.sh
index cfd453a..5fe0c6e 100644
--- a/tests.sh
+++ b/tests.sh
@@ -60,7 +60,7 @@ mount --bind /run/resolvconf/resolv.conf /etc/resolv.conf
 sleep 5
 
 # activate virtualenv
-source $HOME/virtualenv/python2.7/bin/activate
+source $HOME/virtualenv/$VENV/bin/activate
 
 # run the build
 py.test -q tests && behave -c
diff --git a/tests/unit/test_io.py b/tests/unit/test_io.py
index 8f1c791..658c2b0 100644
--- a/tests/unit/test_io.py
+++ b/tests/unit/test_io.py
@@ -15,7 +15,7 @@
 # limitations under the License.
 
 from expects import expect, equal, be_none, be_true, be_false
-from io import StringIO
+from io import StringIO, BytesIO
 import dockerpty.io as io
 
 import sys
@@ -23,6 +23,7 @@
 import fcntl
 import socket
 import tempfile
+import six
 
 
 def test_set_blocking_changes_fd_flags():
@@ -47,9 +48,9 @@ def test_set_blocking_returns_previous_state():
 
 def test_select_returns_streams_for_reading():
         a, b = socket.socketpair()
-        a.send('test')
+        a.send(b'test')
         expect(io.select([a, b], timeout=0)).to(equal([b]))
-        b.send('test')
+        b.send(b'test')
         expect(io.select([a, b], timeout=0)).to(equal([a, b]))
         b.recv(4)
         expect(io.select([a, b], timeout=0)).to(equal([a]))
@@ -63,48 +64,41 @@ def test_fileno_delegates_to_file_descriptor(self):
         stream = io.Stream(sys.stdout)
         expect(stream.fileno()).to(equal(sys.stdout.fileno()))
 
-
     def test_read_from_socket(self):
         a, b = socket.socketpair()
-        a.send('test')
+        a.send(b'test')
         stream = io.Stream(b)
-        expect(stream.read(32)).to(equal('test'))
-
+        expect(stream.read(32)).to(equal(b'test'))
 
     def test_write_to_socket(self):
         a, b = socket.socketpair()
         stream = io.Stream(a)
-        stream.write('test')
-        expect(b.recv(32)).to(equal('test'))
-
+        stream.write(b'test')
+        expect(b.recv(32)).to(equal(b'test'))
 
     def test_read_from_file(self):
         with tempfile.TemporaryFile() as f:
             stream = io.Stream(f)
-            f.write('test')
+            f.write(b'test')
             f.seek(0)
-            expect(stream.read(32)).to(equal('test'))
-
+            expect(stream.read(32)).to(equal(b'test'))
 
     def test_read_returns_empty_string_at_eof(self):
         with tempfile.TemporaryFile() as f:
             stream = io.Stream(f)
-            expect(stream.read(32)).to(equal(''))
-
+            expect(stream.read(32)).to(equal(b''))
 
     def test_write_to_file(self):
         with tempfile.TemporaryFile() as f:
             stream = io.Stream(f)
-            stream.write('test')
+            stream.write(b'test')
             f.seek(0)
-            expect(f.read(32)).to(equal('test'))
-
+            expect(f.read(32)).to(equal(b'test'))
 
     def test_write_returns_length_written(self):
         with tempfile.TemporaryFile() as f:
             stream = io.Stream(f)
-            expect(stream.write('test')).to(equal(4))
-
+            expect(stream.write(b'test')).to(equal(4))
 
     def test_write_returns_none_when_no_data(self):
         stream = io.Stream(StringIO())
@@ -137,64 +131,56 @@ class TestDemuxer(object):
 
     def create_fixture(self):
         chunks = [
-            "\x01\x00\x00\x00\x00\x00\x00\x03foo",
-            "\x01\x00\x00\x00\x00\x00\x00\x01d",
+            b"\x01\x00\x00\x00\x00\x00\x00\x03foo",
+            b"\x01\x00\x00\x00\x00\x00\x00\x01d",
         ]
-        return StringIO(u''.join(chunks))
-
+        return six.BytesIO(six.binary_type().join(chunks))
 
     def test_fileno_delegates_to_stream(self):
         demuxer = io.Demuxer(sys.stdout)
         expect(demuxer.fileno()).to(equal(sys.stdout.fileno()))
 
-
     def test_reading_single_chunk(self):
         demuxer = io.Demuxer(self.create_fixture())
-        expect(demuxer.read(32)).to(equal('foo'))
-
+        expect(demuxer.read(32)).to(equal(b'foo'))
 
     def test_reading_multiple_chunks(self):
         demuxer = io.Demuxer(self.create_fixture())
-        expect(demuxer.read(32)).to(equal('foo'))
-        expect(demuxer.read(32)).to(equal('d'))
-
+        expect(demuxer.read(32)).to(equal(b'foo'))
+        expect(demuxer.read(32)).to(equal(b'd'))
 
     def test_reading_data_from_slow_stream(self):
         slow_stream = SlowStream([
-            "\x01\x00\x00\x00\x00\x00\x00\x03f",
-            "oo",
-            "\x01\x00\x00\x00\x00\x00\x00\x01d",
+            b"\x01\x00\x00\x00\x00\x00\x00\x03f",
+            b"oo",
+            b"\x01\x00\x00\x00\x00\x00\x00\x01d",
         ])
 
         demuxer = io.Demuxer(slow_stream)
-        expect(demuxer.read(32)).to(equal('foo'))
-        expect(demuxer.read(32)).to(equal('d'))
-
+        expect(demuxer.read(32)).to(equal(b'foo'))
+        expect(demuxer.read(32)).to(equal(b'd'))
 
     def test_reading_size_from_slow_stream(self):
         slow_stream = SlowStream([
-            "\x01\x00\x00\x00",
-            "\x00\x00\x00\x03foo",
-            "\x01\x00",
-            "\x00\x00\x00\x00\x00\x01d",
+            b'\x01\x00\x00\x00',
+            b'\x00\x00\x00\x03foo',
+            b'\x01\x00',
+            b'\x00\x00\x00\x00\x00\x01d',
         ])
 
         demuxer = io.Demuxer(slow_stream)
-        expect(demuxer.read(32)).to(equal('foo'))
-        expect(demuxer.read(32)).to(equal('d'))
-
+        expect(demuxer.read(32)).to(equal(b'foo'))
+        expect(demuxer.read(32)).to(equal(b'd'))
 
     def test_reading_partial_chunk(self):
         demuxer = io.Demuxer(self.create_fixture())
-        expect(demuxer.read(2)).to(equal('fo'))
-
+        expect(demuxer.read(2)).to(equal(b'fo'))
 
     def test_reading_overlapping_chunks(self):
         demuxer = io.Demuxer(self.create_fixture())
-        expect(demuxer.read(2)).to(equal('fo'))
-        expect(demuxer.read(2)).to(equal('o'))
-        expect(demuxer.read(2)).to(equal('d'))
-
+        expect(demuxer.read(2)).to(equal(b'fo'))
+        expect(demuxer.read(2)).to(equal(b'o'))
+        expect(demuxer.read(2)).to(equal(b'd'))
 
     def test_write_delegates_to_stream(self):
         s = StringIO()
@@ -214,7 +200,6 @@ def test_fileno_delegates_to_from_stream(self):
         pump = io.Pump(sys.stdout, sys.stderr)
         expect(pump.fileno()).to(equal(sys.stdout.fileno()))
 
-
     def test_flush_pipes_data_between_streams(self):
         a = StringIO(u'food')
         b = StringIO()
@@ -223,7 +208,6 @@ def test_flush_pipes_data_between_streams(self):
         expect(a.read(1)).to(equal('d'))
         expect(b.getvalue()).to(equal('foo'))
 
-
     def test_flush_returns_length_written(self):
         a = StringIO(u'fo')
         b = StringIO()
diff --git a/tests/util.py b/tests/util.py
index c7356fc..6778e41 100644
--- a/tests/util.py
+++ b/tests/util.py
@@ -21,6 +21,7 @@
 import os
 import re
 import time
+import six
 
 
 def set_pty_size(fd, size):
@@ -57,7 +58,6 @@ def write(fd, data):
     """
     Write `data` to the PTY at `fd`.
     """
-
     os.write(fd, data)
 
 
@@ -69,7 +69,7 @@ def readchar(fd):
     while True:
         ready = wait(fd)
         if len(ready) == 0:
-            return ''
+            return six.binary_type()
         else:
             for s in ready:
                 return os.read(s, 1)
@@ -82,15 +82,15 @@ def readline(fd):
     The line includes the line ending.
     """
 
-    output = []
+    output = six.binary_type()
     while True:
         char = readchar(fd)
         if char:
-            output.append(char)
-            if char == "\n":
-                return ''.join(output)
+            output = output + char
+            if char == b"\n":
+                return output
         else:
-            return ''.join(output)
+            return output
 
 
 def read(fd):
@@ -98,13 +98,13 @@ def read(fd):
     Read all output from the PTY at `fd`, or nothing if no data to read.
     """
 
-    output = []
+    output = six.binary_type()
     while True:
         line = readline(fd)
         if line:
-            output.append(line)
+            output = output + line
         else:
-            return "".join(output)
+            return output.decode()
 
 
 def read_printable(fd):
diff --git a/tox.ini b/tox.ini
index 7147097..338182f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,9 +1,11 @@
 [tox]
-envlist = py27, pypy
+envlist = py27, pypy, py33
 
 [testenv]
 deps =
-    -rrequirements-dev.txt
+    py27: -rrequirements-dev.txt
+    pypy: -rrequirements-dev.txt
+    py33: -rrequirements3-dev.txt
 commands =
     py.test -v tests/
     behave