diff --git a/google/auth/_oauth2client.py b/google/auth/_oauth2client.py
new file mode 100644
index 0000000..312326e
--- /dev/null
+++ b/google/auth/_oauth2client.py
@@ -0,0 +1,166 @@
+# Copyright 2016 Google Inc.
+#
+# 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.
+
+"""Helpers for transitioning from oauth2client to google-auth.
+
+.. warning::
+    This module is private as it is intended to assist first-party downstream
+    clients with the transition from oauth2client to google-auth.
+"""
+
+from __future__ import absolute_import
+
+from google.auth import _helpers
+import google.auth.app_engine
+import google.oauth2.credentials
+import google.oauth2.service_account
+
+try:
+    import oauth2client.client
+    import oauth2client.contrib.gce
+    import oauth2client.service_account
+except ImportError:
+    raise ImportError('oauth2client is not installed.')
+
+try:
+    import oauth2client.contrib.appengine
+    _HAS_APPENGINE = True
+except ImportError:
+    _HAS_APPENGINE = False
+
+
+_CONVERT_ERROR_TMPL = (
+    'Unable to convert {} to a google-auth credentials class.')
+
+
+def _convert_oauth2_credentials(credentials):
+    """Converts to :class:`google.oauth2.credentials.Credentials`.
+
+    Args:
+        credentials (Union[oauth2client.client.OAuth2Credentials,
+            oauth2client.client.GoogleCredentials]): The credentials to
+            convert.
+
+    Returns:
+        google.oauth2.credentials.Credentials: The converted credentials.
+    """
+    new_credentials = google.oauth2.credentials.Credentials(
+        token=credentials.access_token,
+        refresh_token=credentials.refresh_token,
+        token_uri=credentials.token_uri,
+        client_id=credentials.client_id,
+        client_secret=credentials.client_secret,
+        scopes=credentials.scopes)
+
+    new_credentials._expires = credentials.token_expiry
+
+    return new_credentials
+
+
+def _convert_service_account_credentials(credentials):
+    """Converts to :class:`google.oauth2.service_account.Credentials`.
+
+    Args:
+        credentials (Union[
+            oauth2client.service_account.ServiceAccountCredentials,
+            oauth2client.service_account._JWTAccessCredentials]): The
+            credentials to convert.
+
+    Returns:
+        google.oauth2.service_account.Credentials: The converted credentials.
+    """
+    info = credentials.serialization_data.copy()
+    info['token_uri'] = credentials.token_uri
+    return google.oauth2.service_account.Credentials.from_service_account_info(
+        info)
+
+
+def _convert_gce_app_assertion_credentials(credentials):
+    """Converts to :class:`google.auth.compute_engine.Credentials`.
+
+    Args:
+        credentials (oauth2client.contrib.gce.AppAssertionCredentials): The
+            credentials to convert.
+
+    Returns:
+        google.oauth2.service_account.Credentials: The converted credentials.
+    """
+    return google.auth.compute_engine.Credentials(
+        service_account_email=credentials.service_account_email)
+
+
+def _convert_appengine_app_assertion_credentials(credentials):
+    """Converts to :class:`google.auth.app_engine.Credentials`.
+
+    Args:
+        credentials (oauth2client.contrib.app_engine.AppAssertionCredentials):
+            The credentials to convert.
+
+    Returns:
+        google.oauth2.service_account.Credentials: The converted credentials.
+    """
+    # pylint: disable=invalid-name
+    return google.auth.app_engine.Credentials(
+        scopes=_helpers.string_to_scopes(credentials.scope),
+        service_account_id=credentials.service_account_id)
+
+
+_CLASS_CONVERSION_MAP = {
+    oauth2client.client.OAuth2Credentials: _convert_oauth2_credentials,
+    oauth2client.client.GoogleCredentials: _convert_oauth2_credentials,
+    oauth2client.service_account.ServiceAccountCredentials:
+        _convert_service_account_credentials,
+    oauth2client.service_account._JWTAccessCredentials:
+        _convert_service_account_credentials,
+    oauth2client.contrib.gce.AppAssertionCredentials:
+        _convert_gce_app_assertion_credentials,
+}
+
+if _HAS_APPENGINE:
+    _CLASS_CONVERSION_MAP[
+        oauth2client.contrib.appengine.AppAssertionCredentials] = (
+            _convert_appengine_app_assertion_credentials)
+
+
+def convert(credentials):
+    """Convert oauth2client credentials to google-auth credentials.
+
+    This class converts:
+
+    - :class:`oauth2client.client.OAuth2Credentials` to
+      :class:`google.oauth2.credentials.Credentials`.
+    - :class:`oauth2client.client.GoogleCredentials` to
+      :class:`google.oauth2.credentials.Credentials`.
+    - :class:`oauth2client.service_account.ServiceAccountCredentials` to
+      :class:`google.oauth2.service_account.Credentials`.
+    - :class:`oauth2client.service_account._JWTAccessCredentials` to
+      :class:`google.oauth2.service_account.Credentials`.
+    - :class:`oauth2client.contrib.gce.AppAssertionCredentials` to
+      :class:`google.auth.compute_engine.Credentials`.
+    - :class:`oauth2client.contrib.appengine.AppAssertionCredentials` to
+      :class:`google.auth.app_engine.Credentials`.
+
+    Returns:
+        google.auth.credentials.Credentials: The converted credentials.
+
+    Raises:
+        ValueError: If the credentials could not be converted.
+    """
+
+    credentials_class = type(credentials)
+
+    try:
+        return _CLASS_CONVERSION_MAP[credentials_class](credentials)
+    except KeyError:
+        raise ValueError(_CONVERT_ERROR_TMPL.format(credentials_class))