diff --git a/google/auth/transport/__init__.py b/google/auth/transport/__init__.py
index 724568e58..56a595d6e 100644
--- a/google/auth/transport/__init__.py
+++ b/google/auth/transport/__init__.py
@@ -4,7 +4,7 @@
 # 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
+#     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,
@@ -12,20 +12,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-"""Transport - HTTP client library support.
-
-:mod:`google.auth` is designed to work with various HTTP client libraries such
-as urllib3 and requests. In order to work across these libraries with different
-interfaces some abstraction is needed.
-
-This module provides two interfaces that are implemented by transport adapters
-to support HTTP libraries. :class:`Request` defines the interface expected by
-:mod:`google.auth` to make requests. :class:`Response` defines the interface
-for the return value of :class:`Request`.
-"""
+"""Transport - HTTP client library support."""
 
 import abc
 import http.client as http_client
+from typing import Mapping, Optional, Any
+
 
 DEFAULT_RETRYABLE_STATUS_CODES = (
     http_client.INTERNAL_SERVER_ERROR,
@@ -33,71 +25,45 @@
     http_client.REQUEST_TIMEOUT,
     http_client.TOO_MANY_REQUESTS,
 )
-"""Sequence[int]:  HTTP status codes indicating a request can be retried.
-"""
-
 
 DEFAULT_REFRESH_STATUS_CODES = (http_client.UNAUTHORIZED,)
-"""Sequence[int]:  Which HTTP status code indicate that credentials should be
-refreshed.
-"""
 
 DEFAULT_MAX_REFRESH_ATTEMPTS = 2
-"""int: How many times to refresh the credentials and retry a request."""
 
 
 class Response(metaclass=abc.ABCMeta):
     """HTTP Response data."""
 
-    @abc.abstractproperty
-    def status(self):
+    @property
+    @abc.abstractmethod
+    def status(self) -> int:
         """int: The HTTP status code."""
-        raise NotImplementedError("status must be implemented.")
+        ...
 
-    @abc.abstractproperty
-    def headers(self):
+    @property
+    @abc.abstractmethod
+    def headers(self) -> Mapping[str, str]:
         """Mapping[str, str]: The HTTP response headers."""
-        raise NotImplementedError("headers must be implemented.")
+        ...
 
-    @abc.abstractproperty
-    def data(self):
+    @property
+    @abc.abstractmethod
+    def data(self) -> bytes:
         """bytes: The response body."""
-        raise NotImplementedError("data must be implemented.")
+        ...
 
 
 class Request(metaclass=abc.ABCMeta):
-    """Interface for a callable that makes HTTP requests.
-
-    Specific transport implementations should provide an implementation of
-    this that adapts their specific request / response API.
-
-    .. automethod:: __call__
-    """
+    """Interface for a callable that makes HTTP requests."""
 
     @abc.abstractmethod
     def __call__(
-        self, url, method="GET", body=None, headers=None, timeout=None, **kwargs
-    ):
-        """Make an HTTP request.
-
-        Args:
-            url (str): The URI to be requested.
-            method (str): The HTTP method to use for the request. Defaults
-                to 'GET'.
-            body (bytes): The payload / body in HTTP request.
-            headers (Mapping[str, str]): Request headers.
-            timeout (Optional[int]): The number of seconds to wait for a
-                response from the server. If not specified or if None, the
-                transport-specific default timeout will be used.
-            kwargs: Additionally arguments passed on to the transport's
-                request method.
-
-        Returns:
-            Response: The HTTP response.
-
-        Raises:
-            google.auth.exceptions.TransportError: If any exception occurred.
-        """
-        # pylint: disable=redundant-returns-doc, missing-raises-doc
-        # (pylint doesn't play well with abstract docstrings.)
-        raise NotImplementedError("__call__ must be implemented.")
+        self,
+        url: str,
+        method: str = "GET",
+        body: Optional[bytes] = None,
+        headers: Optional[Mapping[str, str]] = None,
+        timeout: Optional[int] = None,
+        **kwargs: Any,
+    ) -> Response:
+        ...