diff --git a/.gitignore b/.gitignore
index b0e734a..3c564c7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,11 +1,12 @@
 *.pyc
 *.sw?
 *~
 .coverage
 .eggs/
 __pycache__
 *.egg-info/
 build/
 dist/
 version.txt
 .tox
+.mypy_cache/
diff --git a/mypy.ini b/mypy.ini
new file mode 100644
index 0000000..632d9a8
--- /dev/null
+++ b/mypy.ini
@@ -0,0 +1,12 @@
+[mypy]
+namespace_packages = True
+warn_unused_ignores = True
+
+
+# 3rd party libraries without stubs (yet)
+
+[mypy-pkg_resources.*]
+ignore_missing_imports = True
+
+[mypy-pytest.*]
+ignore_missing_imports = True
diff --git a/swh/__init__.py b/swh/__init__.py
index 69e3be5..de9df06 100644
--- a/swh/__init__.py
+++ b/swh/__init__.py
@@ -1 +1,4 @@
-__path__ = __import__('pkgutil').extend_path(__path__, __name__)
+from typing import Iterable
+
+__path__ = __import__('pkgutil').extend_path(__path__,
+                                             __name__)  # type: Iterable[str]
diff --git a/swh/graph/py.typed b/swh/graph/py.typed
new file mode 100644
index 0000000..1242d43
--- /dev/null
+++ b/swh/graph/py.typed
@@ -0,0 +1 @@
+# Marker file for PEP 561.
diff --git a/tox.ini b/tox.ini
index 0fb07c6..a33e8ce 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,16 +1,24 @@
 [tox]
-envlist=flake8,py3
+envlist=flake8,py3,mypy
 
 [testenv:py3]
 deps =
   .[testing]
   pytest-cov
 commands =
   pytest --cov=swh --cov-branch {posargs}
 
 [testenv:flake8]
 skip_install = true
 deps =
   flake8
 commands =
   {envpython} -m flake8
+
+[testenv:mypy]
+skip_install = true
+deps =
+  .[testing]
+  mypy
+commands =
+  mypy swh