diff --git a/dev_tools/modules.py b/dev_tools/modules.py
index f47e89fcf6c..9fd5ecdbc25 100644
--- a/dev_tools/modules.py
+++ b/dev_tools/modules.py
@@ -22,29 +22,40 @@
 
 listing modules:
  - Python: see list_modules
- - CLI: python3 dev_tools/modules.py list
+
+Version management:
+ - Python: get_version and replace_version
+ - CLI:
+    - python3 dev_tools/modules.py print_version
+    - python3 dev_tools/modules.py replace_version --old v0.12.0.dev --new v0.12.1.dev
 
 optional arguments:
   -h, --help            show this help message and exit
-  --mode {folder,package-path}
-                        'folder' to list root folder for module (e.g. cirq-google),
-                        'package-path' for top level python package path
-                            (e.g. cirq-google/cirq_google),
-                        'package' for top level python package (e.g cirq_google),
-  --include-parent      whether to include the parent package or not
+
+subcommands:
+  valid subcommands
+
+  {list,print_version,replace_version}
+                        additional help
+    list                lists all the modules
+    print_version       Check that all module versions are the same, and print it.
+    replace_version     replace Cirq version in all modules
 """
 
 import argparse
 import dataclasses
 import os
+import re
 import sys
 from pathlib import Path
-from typing import List, Dict, Any
+from typing import List, Dict, Any, Optional
 
 _FOLDER = 'folder'
 _PACKAGE_PATH = 'package-path'
 _PACKAGE = 'package'
 
+_DEFAULT_SEARCH_DIR: Path = Path(".")
+
 
 @dataclasses.dataclass
 class Module:
@@ -71,7 +82,7 @@ def __post_init__(self) -> None:
 
 
 def list_modules(
-    search_dir: Path = Path(__file__).parents[1], include_parent: bool = False
+    search_dir: Path = _DEFAULT_SEARCH_DIR, include_parent: bool = False
 ) -> List[Module]:
     """Returns a list of python modules based defined by setup.py files.
 
@@ -83,6 +94,8 @@ def list_modules(
           a list of `Module`s that were found, where each module `m` is initialized with `m.root`
            relative to `search_dir`, `m.raw_setup` contains the dictionary equivalent to the
            keyword args passed to the `setuptools.setup` method in setup.py
+    Raises:
+        ValueError: if include_parent=True but there is no setup.py in `search_dir`.
     """
 
     relative_folders = sorted(
@@ -92,9 +105,8 @@ def list_modules(
     )
     if include_parent:
         parent_setup_py = search_dir / "setup.py"
-        assert parent_setup_py.exists(), (
-            f"include_parent=True, but {parent_setup_py} " f"does not exist."
-        )
+        if not parent_setup_py.exists():
+            raise ValueError(f"include_parent=True, but {parent_setup_py} does not exist.")
         relative_folders.append(Path("."))
 
     result = [
@@ -105,6 +117,66 @@ def list_modules(
     return result
 
 
+def get_version(search_dir: Path = _DEFAULT_SEARCH_DIR) -> Optional[str]:
+    """Check for all versions are the same and return that version.
+
+    Lists all the modules within `search_dir` (default the current working directory), checks that
+    all of them are the same version and returns that version. If no modules found, None is
+    returned, if more than one, ValueError is raised.
+
+    Args:
+        search_dir: the search directory for modules.
+    Returns:
+        None if no modules are found, the version number if exactly one version number is found.
+    Raises:
+        ValueError: if more than one version numbers are found.
+    """
+    try:
+        mods = list_modules(search_dir=search_dir, include_parent=True)
+    except ValueError:
+        return None
+    versions = {m.name: m.version for m in mods}
+    if len(set(versions.values())) > 1:
+        raise ValueError(f"Versions should be the same, instead: \n{versions}")
+    return list(set(versions.values()))[0]
+
+
+def replace_version(search_dir: Path = _DEFAULT_SEARCH_DIR, *, old: str, new: str):
+    """Replaces the current version number with a new version number.
+
+    Args:
+        search_dir: the search directory for modules.
+        old: the current version number.
+        new: the new version number.
+    Raises:
+        ValueError: if `old` does not match the current version, or if there is not exactly one
+            version number in the found modules.
+    """
+    version = get_version(search_dir=search_dir)
+    if version != old:
+        raise ValueError(f"{old} does not match current version: {version}")
+
+    _validate_version(new)
+
+    for m in list_modules(search_dir=search_dir, include_parent=True):
+        version_file = _find_version_file(search_dir / m.root)
+        content = version_file.read_text("UTF-8")
+        new_content = content.replace(old, new)
+        version_file.write_text(new_content)
+
+
+def _validate_version(new_version: str):
+    if not re.match(r"\d+\.\d+\.\d+(\.dev)?", new_version):
+        raise ValueError(f"{new_version} is not a valid version number.")
+
+
+def _find_version_file(top: Path) -> Path:
+    for root, _, files in os.walk(str(top)):
+        if "_version.py" in files:
+            return Path(root) / "_version.py"
+    raise FileNotFoundError(f"Can't find _version.py in {top}.")
+
+
 def _parse_module(folder: Path) -> Dict[str, Any]:
     setup_args = {}
     import setuptools
@@ -130,6 +202,73 @@ def setup(**kwargs):
         os.chdir(cwd)
 
 
+############################################
+# CLI MANAGEMENT
+############################################
+
+
+# --------------
+# print_version
+# --------------
+
+
+def _print_version():
+    print(get_version())
+
+
+def _add_print_version_cmd(subparsers):
+    print_version_cmd = subparsers.add_parser(
+        "print_version", help="Check that all module versions are the same, " "and print it."
+    )
+    print_version_cmd.set_defaults(func=_print_version)
+
+
+# --------------
+# replace_version
+# --------------
+
+
+def _replace_version(old: str, new: str):
+    replace_version(old=old, new=new)
+    print(f"Successfully replaced version {old} with {new}.")
+
+
+def _add_replace_version_cmd(subparsers):
+    replace_version_cmd = subparsers.add_parser(
+        "replace_version", help="replace Cirq version in all modules"
+    )
+    replace_version_cmd.add_argument(
+        "--old", required=True, help="the current version to be replaced"
+    )
+    replace_version_cmd.add_argument("--new", required=True, help="the new version to be replaced")
+    replace_version_cmd.set_defaults(func=_replace_version)
+
+
+# --------------
+# list_modules
+# --------------
+
+
+def _add_list_modules_cmd(subparsers):
+    list_modules_cmd = subparsers.add_parser("list", help="lists all the modules")
+    list_modules_cmd.add_argument(
+        "--mode",
+        default=_FOLDER,
+        choices=[_FOLDER, _PACKAGE_PATH, _PACKAGE],
+        type=str,
+        help="'folder' to list root folder for module (e.g. cirq-google),\n"
+        "'package-path' for top level python package path (e.g. cirq-google/cirq_google),\n"
+        "'package' for top level python package (e.g cirq_google),\n",
+    )
+    list_modules_cmd.add_argument(
+        "--include-parent",
+        help="whether to include the parent package or not",
+        default=False,
+        action="store_true",
+    )
+    list_modules_cmd.set_defaults(func=_print_list_modules)
+
+
 def _print_list_modules(mode: str, include_parent: bool = False):
     """Prints certain properties of cirq modules on separate lines.
 
@@ -139,9 +278,7 @@ def _print_list_modules(mode: str, include_parent: bool = False):
     Args:
         mode: 'folder' lists the root folder for each module, 'package-path' lists the path to
          the top level package(s).
-        include_cirq: when true the cirq metapackage is included in the list
-    Returns:
-          a list of strings
+        include_parent: when true the cirq metapackage is included in the list
     """
     for m in list_modules(Path("."), include_parent):
         if mode == _FOLDER:
@@ -154,44 +291,26 @@ def _print_list_modules(mode: str, include_parent: bool = False):
                 print(package, end=" ")
 
 
-def main(argv: List[str]):
-    args = parse(argv)
-    # args.func is where we store the function to be called for a given subparser
-    # e.g. it is list_modules for the `list` subcommand
-    f = args.func
-    # however the func is not going to be needed for the function itself, so
-    # we remove it here
-    del args.func
-    f(**vars(args))
-
-
 def parse(args):
     parser = argparse.ArgumentParser('A utility for modules.')
     subparsers = parser.add_subparsers(
         title='subcommands', description='valid subcommands', help='additional help'
     )
     _add_list_modules_cmd(subparsers)
+    _add_print_version_cmd(subparsers)
+    _add_replace_version_cmd(subparsers)
     return parser.parse_args(args)
 
 
-def _add_list_modules_cmd(subparsers):
-    list_modules_cmd = subparsers.add_parser("list", help="lists all the modules")
-    list_modules_cmd.add_argument(
-        "--mode",
-        default=_FOLDER,
-        choices=[_FOLDER, _PACKAGE_PATH, _PACKAGE],
-        type=str,
-        help="'folder' to list root folder for module (e.g. cirq-google),\n"
-        "'package-path' for top level python package path (e.g. cirq-google/cirq_google),\n"
-        "'package' for top level python package (e.g cirq_google),\n",
-    )
-    list_modules_cmd.add_argument(
-        "--include-parent",
-        help="whether to include the parent package or not",
-        default=False,
-        action="store_true",
-    )
-    list_modules_cmd.set_defaults(func=_print_list_modules)
+def main(argv: List[str]):
+    args = parse(argv)
+    # args.func is where we store the function to be called for a given subparser
+    # e.g. it is list_modules for the `list` subcommand
+    f = args.func
+    # however the func is not going to be needed for the function itself, so
+    # we remove it here
+    del args.func
+    f(**vars(args))
 
 
 if __name__ == '__main__':
diff --git a/dev_tools/modules_test.py b/dev_tools/modules_test.py
index 5edf53b82f9..366f14b2731 100644
--- a/dev_tools/modules_test.py
+++ b/dev_tools/modules_test.py
@@ -19,6 +19,7 @@
 import tempfile
 from io import StringIO
 from pathlib import Path
+from typing import Generator
 from unittest import mock
 
 import pytest
@@ -32,7 +33,7 @@ def test_modules():
         root=Path('mod1'),
         raw_setup={
             'name': 'module1',
-            'version': '0.12.0.dev',
+            'version': '1.2.3.dev',
             'url': 'http://github.com/quantumlib/cirq',
             'author': 'The Cirq Developers',
             'author_email': 'cirq-dev@googlegroups.com',
@@ -43,24 +44,26 @@ def test_modules():
         },
     )
     assert mod1.name == 'module1'
-    assert mod1.version == '0.12.0.dev'
+    assert mod1.version == '1.2.3.dev'
     assert mod1.top_level_packages == ['pack1']
     assert mod1.top_level_package_paths == [Path('mod1') / 'pack1']
     assert mod1.install_requires == ['req1', 'req2']
 
     mod2 = Module(
-        root=Path('mod2'), raw_setup={'name': 'module2', 'version': '1.2.3', 'packages': ['pack2']}
+        root=Path('mod2'),
+        raw_setup={'name': 'module2', 'version': '1.2.3.dev', 'packages': ['pack2']},
     )
 
     assert mod2.name == 'module2'
-    assert mod2.version == '1.2.3'
+    assert mod2.version == '1.2.3.dev'
     assert mod2.top_level_packages == ['pack2']
     assert mod2.top_level_package_paths == [Path('mod2') / 'pack2']
     assert mod2.install_requires == []
     assert modules.list_modules(search_dir=Path("dev_tools/modules_test_data")) == [mod1, mod2]
 
     parent = Module(
-        root=Path('.'), raw_setup={'name': 'parent-module', 'version': '1.2.3', 'requirements': []}
+        root=Path('.'),
+        raw_setup={'name': 'parent-module', 'version': '1.2.3.dev', 'requirements': []},
     )
     assert parent.top_level_packages == []
     assert modules.list_modules(
@@ -84,16 +87,23 @@ def test_cli():
 
 
 @contextlib.contextmanager
-def chdir(*, target_dir: str = None):
+def chdir(*, target_dir: str = None, clone_dir: str = None) -> Generator[None, None, None]:
     """Changes for the duration of the test the working directory.
 
     Args:
         target_dir: the target directory. If None is specified, it will create a temporary
             directory.
+        clone_dir: a directory to clone into target_dir.
+    Yields:
+        None
     """
 
     cwd = os.getcwd()
     tdir = tempfile.mkdtemp() if target_dir is None else target_dir
+    if clone_dir is not None:
+        if Path(tdir).is_dir():
+            shutil.rmtree(tdir)
+        shutil.copytree(clone_dir, tdir)
     os.chdir(tdir)
     try:
         yield
@@ -120,6 +130,51 @@ def test_main():
         assert output.getvalue() == ' '.join(["pack1", "pack2", ""])
 
 
+@chdir(clone_dir="dev_tools/modules_test_data")
+def test_main_replace_version():
+    with mock.patch('sys.stdout', new=StringIO()) as output:
+        modules.main(["print_version"])
+        assert output.getvalue() == '1.2.3.dev\n'
+
+    with mock.patch('sys.stdout', new=StringIO()) as output:
+        modules.main(["replace_version", "--old", "1.2.3.dev", "--new", "1.2.4.dev"])
+        assert output.getvalue() == 'Successfully replaced version 1.2.3.dev with 1.2.4.dev.\n'
+
+    with mock.patch('sys.stdout', new=StringIO()) as output:
+        modules.main(["print_version"])
+        assert output.getvalue() == '1.2.4.dev\n'
+
+
+@chdir()
+def test_get_version_on_no_modules():
+    # no modules is no version
+    assert modules.get_version() is None
+
+
+@chdir(clone_dir="dev_tools/modules_test_data")
+def test_get_version_on_inconsistent_version_modules():
+    modules.replace_version(search_dir=Path("./mod2"), old="1.2.3.dev", new="1.2.4.dev")
+    assert modules.get_version(search_dir=Path("./mod2")) == "1.2.4.dev"
+    with pytest.raises(ValueError, match=f"Versions should be the same, instead:"):
+        modules.get_version(search_dir=Path("."))
+
+
+@chdir(clone_dir="dev_tools/modules_test_data")
+def test_replace_version(tmpdir_factory):
+    assert modules.get_version() == "1.2.3.dev"
+    modules.replace_version(old="1.2.3.dev", new="1.2.4.dev")
+    assert modules.get_version() == "1.2.4.dev"
+
+
+@chdir(target_dir="dev_tools/modules_test_data")
+def test_replace_version_errors():
+    with pytest.raises(ValueError, match="does not match current version"):
+        modules.replace_version(old="v0.11.0", new="v0.11.1")
+
+    with pytest.raises(ValueError, match="va.b.c is not a valid version number"):
+        modules.replace_version(old="1.2.3.dev", new="va.b.c")
+
+
 @chdir(target_dir=None)
 def test_error():
     f = open("setup.py", mode='w')
diff --git a/dev_tools/modules_test_data/mod1/pack1/_version.py b/dev_tools/modules_test_data/mod1/pack1/_version.py
index 941bf941f5d..c2a42ee7603 100644
--- a/dev_tools/modules_test_data/mod1/pack1/_version.py
+++ b/dev_tools/modules_test_data/mod1/pack1/_version.py
@@ -14,4 +14,4 @@
 
 """Define version number here, read it from setup.py automatically"""
 
-__version__ = "0.12.0.dev"
+__version__ = "1.2.3.dev"
diff --git a/dev_tools/modules_test_data/mod2/pack2/_version.py b/dev_tools/modules_test_data/mod2/pack2/_version.py
index 941bf941f5d..c2a42ee7603 100644
--- a/dev_tools/modules_test_data/mod2/pack2/_version.py
+++ b/dev_tools/modules_test_data/mod2/pack2/_version.py
@@ -14,4 +14,4 @@
 
 """Define version number here, read it from setup.py automatically"""
 
-__version__ = "0.12.0.dev"
+__version__ = "1.2.3.dev"
diff --git a/dev_tools/modules_test_data/mod2/setup.py b/dev_tools/modules_test_data/mod2/setup.py
index 719d454d708..f13f87c1754 100644
--- a/dev_tools/modules_test_data/mod2/setup.py
+++ b/dev_tools/modules_test_data/mod2/setup.py
@@ -2,4 +2,9 @@
 
 name = 'module2'
 
-setup(name=name, version='1.2.3', packages=['pack2'])
+__version__ = ''
+
+
+exec(open('pack2/_version.py').read())
+
+setup(name=name, version=__version__, packages=['pack2'])
diff --git a/dev_tools/modules_test_data/setup.py b/dev_tools/modules_test_data/setup.py
index 5820171c7c6..0fecde6e6d0 100644
--- a/dev_tools/modules_test_data/setup.py
+++ b/dev_tools/modules_test_data/setup.py
@@ -2,4 +2,8 @@
 
 name = 'parent-module'
 
-setup(name=name, version='1.2.3', requirements=[])
+__version__ = ''
+
+exec(open('mod1/pack1/_version.py').read())
+
+setup(name=name, version=__version__, requirements=[])
diff --git a/release.md b/release.md
index 83127e219cd..4bdf2bbc308 100644
--- a/release.md
+++ b/release.md
@@ -105,11 +105,9 @@ git cherry-pick <commit>
 Bump the version on the release branch: 
 
 ```bash
-vi ./cirq-core/cirq/_version.py   # Remove .dev from version
-vi ./cirq-google/cirq_google/_version.py  # Remove .dev from version   
-vi ./cirq-aqt/cirq_aqt/_version.py  # Remove .dev from version   
-git add ./cirq-core/cirq/_version.py ./cirq-google/cirq_google/_version.py
-git commit -m "Bump cirq version to ${NEXT_VER}"
+python dev_tools/modules.py replace_version --old ${VER}.dev --new ${VER} 
+git add .
+git commit -m "Removing ${VER}.dev -> ${VER}"
 git push origin "v${VER}-dev"
 ```
 
@@ -120,8 +118,7 @@ updates, leave it as it is.
 
 ```bash
 git checkout master -b "version_bump_${NEXT_VER}"
-vi ./cirq/_version.py # Bump version to next version.  KEEP .dev!
-git add ./cirq/_version.py
+python dev_tools/modules.py replace_version --old ${VER}.dev --new ${NEXT_VER}.dev
 git commit -m "Bump cirq version to ${NEXT_VER}"
 git push origin "version_bump_${NEXT_VER}"
 ```
@@ -136,7 +133,7 @@ that will go to pypi.
 ```bash
 git checkout "v${VER}-dev"
 ./dev_tools/packaging/produce-package.sh dist
-ls dist  # should only contain 3 files, one versioned whl file for cirq, cirq_google and cirq_core 
+ls dist  # should only contain one file, for each modules 
 ```
 
 ### Push to test pypi