diff --git a/ActivityRepositoryInterface.php b/ActivityRepositoryInterface.php
new file mode 100644
index 0000000..07bd0ab
--- /dev/null
+++ b/ActivityRepositoryInterface.php
@@ -0,0 +1,26 @@
+<?php
+
+namespace XApi\Repository\Api;
+
+use Xabbuh\XApi\Common\Exception\NotFoundException;
+use Xabbuh\XApi\Model\Activity;
+use Xabbuh\XApi\Model\IRI;
+
+/**
+ * Public API of an Experience API (xAPI) {@link Activity} repository.
+ *
+ * @author Jérôme Parmentier <jerome.parmentier@acensi.fr>
+ */
+interface ActivityRepositoryInterface
+{
+    /**
+     * Finds a {@link Activity} by id.
+     *
+     * @param IRI $activityId The activity id to filter by
+     *
+     * @return Activity The activity
+     *
+     * @throws NotFoundException if no Activity with the given IRI does exist
+     */
+    public function findActivityById(IRI $activityId);
+}
diff --git a/CHANGELOG.md b/CHANGELOG.md
index f6ebb1a..6af2eb3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,8 @@ CHANGELOG
 
 * made the package compatible with `3.x` releases of `ramsey/uuid`
 * allow `2.x` releases of the `php-xapi/model` package too
+* Added a `ActivityRepositoryInterface` that defines the public API of a
+  activity repository.
 
 0.3.0
 -----
diff --git a/Test/Functional/ActivityRepositoryTest.php b/Test/Functional/ActivityRepositoryTest.php
new file mode 100644
index 0000000..ed25581
--- /dev/null
+++ b/Test/Functional/ActivityRepositoryTest.php
@@ -0,0 +1,75 @@
+<?php
+
+/*
+ * This file is part of the xAPI package.
+ *
+ * (c) Christian Flothmann <christian.flothmann@xabbuh.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace XApi\Repository\Api\Test\Functional;
+
+use Xabbuh\XApi\Model\Activity;
+use Xabbuh\XApi\Model\IRI;
+use XApi\Repository\Api\ActivityRepositoryInterface;
+
+/**
+ * @author Jérôme Parmentier <jerome.parmentier@acensi.fr>
+ */
+abstract class ActivityRepositoryTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @var ActivityRepositoryInterface
+     */
+    private $activityRepository;
+
+    protected function setUp()
+    {
+        $this->activityRepository = $this->createActivityRepository();
+        $this->cleanDatabase();
+    }
+
+    protected function tearDown()
+    {
+        $this->cleanDatabase();
+    }
+
+    /**
+     * @expectedException \Xabbuh\XApi\Common\Exception\NotFoundException
+     */
+    public function testFetchingNonExistingActivityThrowsException()
+    {
+        $this->activityRepository->findActivityById(IRI::fromString('not-existing'));
+    }
+
+    /**
+     * @dataProvider getStatementsWithId
+     */
+    public function testActivitiesCanBeRetrievedById(Activity $activity)
+    {
+        $fetchedActivity = $this->activityRepository->findActivityById($activity->getId());
+
+        $this->assertTrue($activity->equals($fetchedActivity));
+    }
+
+    public function getActivitiesWithId()
+    {
+        $fixtures = array();
+
+        foreach (get_class_methods('Xabbuh\XApi\DataFixtures\ActivityFixtures') as $method) {
+            $activity = call_user_func(array('Xabbuh\XApi\DataFixtures\ActivityFixtures', $method));
+
+            if ($activity instanceof Activity) {
+                $fixtures[$method] = array($activity);
+            }
+        }
+
+        return $fixtures;
+    }
+
+    abstract protected function createActivityRepository();
+
+    abstract protected function cleanDatabase();
+}