diff --git a/.coveragerc b/.coveragerc
index ce75f60..c6430d3 100644
--- a/.coveragerc
+++ b/.coveragerc
@@ -3,9 +3,9 @@ branch = True
 
 [report]
 omit =
-    google/cloud/_testing.py
     google/cloud/__init__.py
-    google/cloud/environment_vars.py
+    google/cloud/_testing/__init__.py
+    google/cloud/environment_vars/__init__.py
 fail_under = 100
 show_missing = True
 exclude_lines =
diff --git a/google/__init__.py b/google/__init__.py
index 0d0a4c3..70a7bd9 100644
--- a/google/__init__.py
+++ b/google/__init__.py
@@ -21,4 +21,4 @@
 except ImportError:
     import pkgutil
 
-    __path__ = pkgutil.extend_path(__path__, __name__)
+    __path__ = pkgutil.extend_path(__path__, __name__)  # type: ignore
diff --git a/google/cloud/__init__.py b/google/cloud/__init__.py
index f281ec0..ef78099 100644
--- a/google/cloud/__init__.py
+++ b/google/cloud/__init__.py
@@ -21,4 +21,4 @@
 except ImportError:
     import pkgutil
 
-    __path__ = pkgutil.extend_path(__path__, __name__)
+    __path__ = pkgutil.extend_path(__path__, __name__)  # type: ignore
diff --git a/google/cloud/_helpers.py b/google/cloud/_helpers/__init__.py
similarity index 99%
rename from google/cloud/_helpers.py
rename to google/cloud/_helpers/__init__.py
index d8f2851..291f587 100644
--- a/google/cloud/_helpers.py
+++ b/google/cloud/_helpers/__init__.py
@@ -25,6 +25,7 @@
 import os
 import re
 from threading import local as Local
+from typing import Union
 
 import google.auth
 import google.auth.transport.requests
@@ -62,6 +63,7 @@
 )
 # NOTE: Catching this ImportError is a workaround for GAE not supporting the
 #       "pwd" module which is imported lazily when "expanduser" is called.
+_USER_ROOT: Union[str, None]
 try:
     _USER_ROOT = os.path.expanduser("~")
 except ImportError:  # pragma: NO COVER
diff --git a/google/cloud/_helpers/py.typed b/google/cloud/_helpers/py.typed
new file mode 100644
index 0000000..dfc5374
--- /dev/null
+++ b/google/cloud/_helpers/py.typed
@@ -0,0 +1,2 @@
+# Marker file for PEP 561.
+# This package uses inline types.
diff --git a/google/cloud/_http.py b/google/cloud/_http/__init__.py
similarity index 100%
rename from google/cloud/_http.py
rename to google/cloud/_http/__init__.py
diff --git a/google/cloud/_http/py.typed b/google/cloud/_http/py.typed
new file mode 100644
index 0000000..dfc5374
--- /dev/null
+++ b/google/cloud/_http/py.typed
@@ -0,0 +1,2 @@
+# Marker file for PEP 561.
+# This package uses inline types.
diff --git a/google/cloud/_testing.py b/google/cloud/_testing/__init__.py
similarity index 100%
rename from google/cloud/_testing.py
rename to google/cloud/_testing/__init__.py
diff --git a/google/cloud/_testing/py.typed b/google/cloud/_testing/py.typed
new file mode 100644
index 0000000..dfc5374
--- /dev/null
+++ b/google/cloud/_testing/py.typed
@@ -0,0 +1,2 @@
+# Marker file for PEP 561.
+# This package uses inline types.
diff --git a/google/cloud/client.py b/google/cloud/client/__init__.py
similarity index 99%
rename from google/cloud/client.py
rename to google/cloud/client/__init__.py
index e058c2d..b3ca4b8 100644
--- a/google/cloud/client.py
+++ b/google/cloud/client/__init__.py
@@ -18,6 +18,8 @@
 import json
 import os
 from pickle import PicklingError
+from typing import Tuple
+from typing import Union
 
 import google.api_core.client_options
 import google.api_core.exceptions
@@ -142,7 +144,7 @@ class Client(_ClientFactoryMixin):
             to acquire default credentials.
     """
 
-    SCOPE = None
+    SCOPE: Union[Tuple[str], None] = None
     """The scopes required for authenticating with a service.
 
     Needs to be set by subclasses.
diff --git a/google/cloud/client/py.typed b/google/cloud/client/py.typed
new file mode 100644
index 0000000..dfc5374
--- /dev/null
+++ b/google/cloud/client/py.typed
@@ -0,0 +1,2 @@
+# Marker file for PEP 561.
+# This package uses inline types.
diff --git a/google/cloud/environment_vars.py b/google/cloud/environment_vars/__init__.py
similarity index 100%
rename from google/cloud/environment_vars.py
rename to google/cloud/environment_vars/__init__.py
diff --git a/google/cloud/environment_vars/py.typed b/google/cloud/environment_vars/py.typed
new file mode 100644
index 0000000..dfc5374
--- /dev/null
+++ b/google/cloud/environment_vars/py.typed
@@ -0,0 +1,2 @@
+# Marker file for PEP 561.
+# This package uses inline types.
diff --git a/google/cloud/exceptions.py b/google/cloud/exceptions/__init__.py
similarity index 100%
rename from google/cloud/exceptions.py
rename to google/cloud/exceptions/__init__.py
diff --git a/google/cloud/exceptions/py.typed b/google/cloud/exceptions/py.typed
new file mode 100644
index 0000000..dfc5374
--- /dev/null
+++ b/google/cloud/exceptions/py.typed
@@ -0,0 +1,2 @@
+# Marker file for PEP 561.
+# This package uses inline types.
diff --git a/google/cloud/obsolete.py b/google/cloud/obsolete/__init__.py
similarity index 100%
rename from google/cloud/obsolete.py
rename to google/cloud/obsolete/__init__.py
diff --git a/google/cloud/obsolete/py.typed b/google/cloud/obsolete/py.typed
new file mode 100644
index 0000000..dfc5374
--- /dev/null
+++ b/google/cloud/obsolete/py.typed
@@ -0,0 +1,2 @@
+# Marker file for PEP 561.
+# This package uses inline types.
diff --git a/google/cloud/operation.py b/google/cloud/operation/__init__.py
similarity index 99%
rename from google/cloud/operation.py
rename to google/cloud/operation/__init__.py
index 28ac8cf..4fd1f27 100644
--- a/google/cloud/operation.py
+++ b/google/cloud/operation/__init__.py
@@ -14,13 +14,15 @@
 
 """Wrap long-running operations returned from Google Cloud APIs."""
 
+from typing import Dict
+
 from google.longrunning import operations_pb2
 from google.protobuf import json_format
 
 
 _GOOGLE_APIS_PREFIX = "type.googleapis.com"
 
-_TYPE_URL_MAP = {}
+_TYPE_URL_MAP: Dict[str, type] = {}
 
 
 def _compute_type_url(klass, prefix=_GOOGLE_APIS_PREFIX):
diff --git a/google/cloud/operation/py.typed b/google/cloud/operation/py.typed
new file mode 100644
index 0000000..dfc5374
--- /dev/null
+++ b/google/cloud/operation/py.typed
@@ -0,0 +1,2 @@
+# Marker file for PEP 561.
+# This package uses inline types.
diff --git a/mypy.ini b/mypy.ini
new file mode 100644
index 0000000..5663b40
--- /dev/null
+++ b/mypy.ini
@@ -0,0 +1,7 @@
+[mypy]
+python_version = 3.6
+namespace_packages = True
+ignore_missing_imports = True
+
+[mypy-google.protobuf]
+ignore_missing_imports = True
diff --git a/noxfile.py b/noxfile.py
index c29d0f3..8fc781f 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -38,6 +38,16 @@ def lint(session):
     session.run("flake8", "google", "tests")
 
 
+@nox.session(python=DEFAULT_PYTHON_VERSION)
+def mypy(session):
+    """Run type-checking."""
+    session.install(".", "mypy")
+    session.install(
+        "types-setuptools", "types-requests", "types-mock", "types-protobuf",
+    )
+    session.run("mypy", "google", "tests")
+
+
 @nox.session(python=DEFAULT_PYTHON_VERSION)
 def blacken(session):
     """Run black.