diff --git a/google/auth/transport/grpc.py b/google/auth/transport/grpc.py
index 81d5658..8554ffa 100644
--- a/google/auth/transport/grpc.py
+++ b/google/auth/transport/grpc.py
@@ -16,7 +16,12 @@
 
 from __future__ import absolute_import
 
-import grpc
+try:
+    import grpc
+except ImportError:  # pragma: NO COVER
+    raise ImportError(
+        'gRPC is not installed, please install the grpcio package to use the '
+        'gRPC transport.')
 import six
 
 
diff --git a/google/auth/transport/requests.py b/google/auth/transport/requests.py
index e211090..0c66fdd 100644
--- a/google/auth/transport/requests.py
+++ b/google/auth/transport/requests.py
@@ -18,8 +18,12 @@
 
 import logging
 
-
-import requests
+try:
+    import requests
+except ImportError:  # pragma: NO COVER
+    raise ImportError(
+        'The requests library is not installed, please install the requests '
+        'package to use the requests transport.')
 import requests.exceptions
 
 from google.auth import exceptions
diff --git a/google/auth/transport/urllib3.py b/google/auth/transport/urllib3.py
index 9d417b5..a08f427 100644
--- a/google/auth/transport/urllib3.py
+++ b/google/auth/transport/urllib3.py
@@ -30,7 +30,12 @@
 except ImportError:  # pragma: NO COVER
     certifi = None
 
-import urllib3
+try:
+    import urllib3
+except ImportError:  # pragma: NO COVER
+    raise ImportError(
+        'The urllib3 library is not installed, please install the urllib3 '
+        'package to use the urllib3 transport.')
 import urllib3.exceptions
 
 from google.auth import exceptions
diff --git a/google/oauth2/oauthlib.py b/google/oauth2/oauthlib.py
index 8f5c105..e1c6089 100644
--- a/google/oauth2/oauthlib.py
+++ b/google/oauth2/oauthlib.py
@@ -27,7 +27,12 @@
 
 import json
 
-import requests_oauthlib
+try:
+    import requests_oauthlib
+except ImportError:  # pragma: NO COVER
+    raise ImportError(
+        'The requests-oauthlib library is not installed, please install the '
+        'requests-oauthlib package to use google.oauth2.oauthlib.')
 
 import google.oauth2.credentials