diff --git a/.gitignore b/.gitignore
--- a/.gitignore
+++ b/.gitignore
@@ -11,3 +11,4 @@
 version.txt
 .tox
 .hypothesis
+.mypy_cache/
diff --git a/mypy.ini b/mypy.ini
new file mode 100644
--- /dev/null
+++ b/mypy.ini
@@ -0,0 +1,36 @@
+[mypy]
+namespace_packages = True
+warn_unused_ignores = True
+
+
+# 3rd party libraries without stubs (yet)
+
+[mypy-aiohttp_utils.*]
+ignore_missing_imports = True
+
+[mypy-arrow.*]
+ignore_missing_imports = True
+
+[mypy-celery.*]
+ignore_missing_imports = True
+
+[mypy-decorator.*]
+ignore_missing_imports = True
+
+[mypy-deprecated.*]
+ignore_missing_imports = True
+
+[mypy-msgpack.*]
+ignore_missing_imports = True
+
+[mypy-pkg_resources.*]
+ignore_missing_imports = True
+
+[mypy-psycopg2.*]
+ignore_missing_imports = True
+
+[mypy-pytest.*]
+ignore_missing_imports = True
+
+[mypy-systemd.*]
+ignore_missing_imports = True
diff --git a/swh/__init__.py b/swh/__init__.py
--- 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/core/api/__init__.py b/swh/core/api/__init__.py
--- a/swh/core/api/__init__.py
+++ b/swh/core/api/__init__.py
@@ -12,6 +12,8 @@
 import requests
 import datetime
 
+from typing import ClassVar, Optional, Type
+
 from deprecated import deprecated
 from flask import Flask, Request, Response, request, abort
 from .serializers import (decode_response,
@@ -140,7 +142,7 @@
 
     """
 
-    backend_class = None
+    backend_class = None  # type: ClassVar[Optional[type]]
     """For each method of `backend_class` decorated with
     :func:`remote_api_endpoint`, a method with the same prototype and
     docstring will be added to this class. Calls to this new method will
@@ -149,7 +151,7 @@
     This backend class will never be instantiated, it only serves as
     a template."""
 
-    api_exception = APIError
+    api_exception = APIError  # type: ClassVar[Type[Exception]]
     """The exception class to raise in case of communication error with
     the server."""
 
diff --git a/swh/core/api/negotiation.py b/swh/core/api/negotiation.py
--- a/swh/core/api/negotiation.py
+++ b/swh/core/api/negotiation.py
@@ -24,9 +24,10 @@
 #
 
 from collections import defaultdict
+from decorator import decorator
 from inspect import getcallargs
 
-from decorator import decorator
+from typing import Any, List, Optional
 
 
 class FormatterNotFound(Exception):
@@ -34,8 +35,8 @@
 
 
 class Formatter:
-    format = None
-    mimetypes = []
+    format = None  # type: Optional[str]
+    mimetypes = []  # type: List[Any]
 
     def __init__(self, request_mimetype=None):
         if request_mimetype is None or request_mimetype not in self.mimetypes:
diff --git a/swh/core/api/tests/test_api.py b/swh/core/api/tests/test_api.py
--- a/swh/core/api/tests/test_api.py
+++ b/swh/core/api/tests/test_api.py
@@ -5,7 +5,7 @@
 
 import unittest
 
-import requests_mock
+import requests_mock  # type: ignore
 from werkzeug.wrappers import BaseResponse
 from werkzeug.test import Client as WerkzeugTestClient
 
diff --git a/swh/core/api/tests/test_async.py b/swh/core/api/tests/test_async.py
--- a/swh/core/api/tests/test_async.py
+++ b/swh/core/api/tests/test_async.py
@@ -4,9 +4,8 @@
 # See top-level LICENSE file for more information
 
 import datetime
-import json
-
 import msgpack
+import json
 
 import pytest
 
diff --git a/swh/core/config.py b/swh/core/config.py
--- a/swh/core/config.py
+++ b/swh/core/config.py
@@ -10,6 +10,8 @@
 from itertools import chain
 from copy import deepcopy
 
+from typing import Any, Dict, Optional, Tuple
+
 
 logger = logging.getLogger(__name__)
 
@@ -311,8 +313,8 @@
 
     """
 
-    DEFAULT_CONFIG = {}
-    CONFIG_BASE_FILENAME = ''
+    DEFAULT_CONFIG = {}  # type: Dict[str, Tuple[str, Any]]
+    CONFIG_BASE_FILENAME = ''  # type: Optional[str]
 
     @classmethod
     def parse_config_file(cls, base_filename=None, config_filename=None,
diff --git a/swh/core/db/tests/db_testing.py b/swh/core/db/tests/db_testing.py
--- a/swh/core/db/tests/db_testing.py
+++ b/swh/core/db/tests/db_testing.py
@@ -9,9 +9,12 @@
 
 import psycopg2
 
+from typing import Dict, Iterable, Optional, Tuple, Union
+
 from swh.core.utils import numfile_sortkey as sortkey
 
-DB_DUMP_TYPES = {'.sql': 'psql', '.dump': 'pg_dump'}
+
+DB_DUMP_TYPES = {'.sql': 'psql', '.dump': 'pg_dump'}  # type: Dict[str, str]
 
 
 def swh_db_version(dbname_or_service):
@@ -207,8 +210,8 @@
 
     """
 
-    _DB_DUMP_LIST = {}
-    _DB_LIST = {}
+    _DB_DUMP_LIST = {}  # type: Dict[str, Iterable[Tuple[str, str]]]
+    _DB_LIST = {}  # type: Dict[str, DbTestContext]
     DB_TEST_FIXTURE_IMPORTED = True
 
     @classmethod
@@ -286,7 +289,7 @@
     """
 
     TEST_DB_NAME = 'softwareheritage-test'
-    TEST_DB_DUMP = None
+    TEST_DB_DUMP = None  # type: Optional[Union[str, Iterable[str]]]
 
     @classmethod
     def setUpClass(cls):
diff --git a/swh/core/py.typed b/swh/core/py.typed
new file mode 100644
--- /dev/null
+++ b/swh/core/py.typed
@@ -0,0 +1 @@
+# Marker file for PEP 561.
diff --git a/tox.ini b/tox.ini
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist=flake8,py3-{core,db,server}
+envlist=flake8,py3-{core,db,server},mypy
 
 [testenv:py3-core]
 deps =
@@ -42,3 +42,12 @@
   flake8
 commands =
   {envpython} -m flake8
+
+[testenv:mypy]
+skip_install = true
+deps =
+  .[testing]
+  mypy
+  django-stubs
+commands =
+  mypy swh