diff --git a/src/Activities/AnnounceHandler.php b/src/Activities/AnnounceHandler.php
new file mode 100644
index 0000000..055368d
--- /dev/null
+++ b/src/Activities/AnnounceHandler.php
@@ -0,0 +1,78 @@
+<?php
+
+namespace ActivityPub\Activities;
+
+use ActivityPub\Entities\ActivityPubObject;
+use ActivityPub\Objects\CollectionsService;
+use ActivityPub\Objects\ContextProvider;
+use ActivityPub\Objects\ObjectsService;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+use Symfony\Component\HttpKernel\Exception\BadRequestHttpException;
+
+class AnnounceHandler implements EventSubscriberInterface
+{
+    /**
+     * @var ObjectsService
+     */
+    private $objectsService;
+
+    /**
+     * @var CollectionsService
+     */
+    private $collectionsService;
+
+    /**
+     * @var ContextProvider
+     */
+    private $contextProvider;
+
+    public static function getSubscribedEvents()
+    {
+        return array(
+            InboxActivityEvent::NAME => 'handleInbox',
+        );
+    }
+
+    public function __construct( ObjectsService $objectsService,
+                                 CollectionsService $collectionsService,
+                                 ContextProvider $contextProvider )
+    {
+        $this->objectsService = $objectsService;
+        $this->collectionsService = $collectionsService;
+        $this->contextProvider = $contextProvider;
+    }
+
+    public function handleInbox( InboxActivityEvent $event )
+    {
+        $activity = $event->getActivity();
+        if ( $activity['type'] !== 'Announce' ) {
+            return;
+        }
+        $objectId = $activity['object'];
+        if ( is_array( $objectId ) && array_key_exists( 'id', $objectId ) ) {
+            $objectId = $objectId['id'];
+        }
+        if ( ! is_string( $objectId ) ) {
+            throw new BadRequestHttpException( 'Invalid object' );
+        }
+        $object = $this->objectsService->dereference( $objectId );
+        if ( ! $object->hasField( 'shares' ) ) {
+            $object = $this->addCollectionToObject( $object, 'shares' );
+
+        }
+        $shares = $object['shares'];
+        $this->collectionsService->addItem( $shares, $activity );
+    }
+
+    private function addCollectionToObject( ActivityPubObject $object, $collectionName )
+    {
+        $updatedObject = $object->asArray();
+        $updatedObject[$collectionName] = array(
+            '@context' => $this->contextProvider->getContext(),
+            'id' => rtrim( $updatedObject['id'], '/' ) . '/' . $collectionName,
+            'type' => 'Collection',
+            'items' => array(),
+        );
+        return $this->objectsService->update( $object['id'], $updatedObject );
+    }
+}
\ No newline at end of file
diff --git a/test/Activities/AnnounceHandlerTest.php b/test/Activities/AnnounceHandlerTest.php
new file mode 100644
index 0000000..c3bf110
--- /dev/null
+++ b/test/Activities/AnnounceHandlerTest.php
@@ -0,0 +1,125 @@
+<?php
+
+namespace ActivityPub\Test\Activities;
+
+use ActivityPub\Activities\AnnounceHandler;
+use ActivityPub\Activities\InboxActivityEvent;
+use ActivityPub\Objects\CollectionsService;
+use ActivityPub\Objects\ContextProvider;
+use ActivityPub\Objects\ObjectsService;
+use ActivityPub\Test\TestConfig\APTestCase;
+use ActivityPub\Test\TestUtils\TestActivityPubObject;
+use Symfony\Component\EventDispatcher\EventDispatcher;
+
+class AnnounceHandlerTest extends APTestCase
+{
+    private static function getObjects()
+    {
+        return array(
+            'https://example.com/notes/withshares' => array(
+                'id' => 'https://example.com/notes/withshares',
+                'shares' => array(
+                    'type' => 'Collection',
+                    'items' => array(),
+                ),
+            ),
+            'https://example.com/notes/withoutshares' => array(
+                'id' => 'https://example.com/notes/withoutshares',
+            ),
+        );
+    }
+
+    public function testAnnounceHandler()
+    {
+        $testCases = array(
+            array(
+                'id' => 'basicInboxTest',
+                'eventName' => InboxActivityEvent::NAME,
+                'event' => new InboxActivityEvent(
+                    array(
+                        'id' => 'https://elsewhere.com/announces/1',
+                        'type' => 'Announce',
+                        'object' => 'https://example.com/notes/withshares',
+                    ),
+                    TestActivityPubObject::fromArray( array(
+                        'id' => 'https://example.com/actors/1',
+                    ) ),
+                    self::requestWithAttributes(
+                        'https://example.com/actors/1/inbox',
+                        array(
+                            'actor' => TestActivityPubObject::fromArray( array(
+                                'id' => 'https://elsewhere.com/actors/1',
+                            ) ),
+                        )
+                    )
+                ),
+                'expectedNewShares' => array(
+                    'id' => 'https://elsewhere.com/announces/1',
+                    'type' => 'Announce',
+                    'object' => 'https://example.com/notes/withshares',
+                )
+            ),
+            array(
+                'id' => 'generatesSharesCollectionTest',
+                'eventName' => InboxActivityEvent::NAME,
+                'event' => new InboxActivityEvent(
+                    array(
+                        'id' => 'https://elsewhere.com/announces/1',
+                        'type' => 'Announce',
+                        'object' => 'https://example.com/notes/withoutshares',
+                    ),
+                    TestActivityPubObject::fromArray( array(
+                        'id' => 'https://example.com/actors/1',
+                    ) ),
+                    self::requestWithAttributes(
+                        'https://example.com/actors/1/inbox',
+                        array(
+                            'actor' => TestActivityPubObject::fromArray( array(
+                                'id' => 'https://elsewhere.com/actors/1',
+                            ) ),
+                        )
+                    )
+                ),
+                'expectedNewShares' => array(
+                    'id' => 'https://elsewhere.com/announces/1',
+                    'type' => 'Announce',
+                    'object' => 'https://example.com/notes/withoutshares',
+                )
+            ),
+        );
+        foreach( $testCases as $testCase ) {
+            $objectsService = $this->getMock( ObjectsService::class );
+            $objectsService->method( 'dereference')->willReturnCallback( function( $id ) {
+                $objects = self::getObjects();
+                if ( array_key_exists( $id, $objects ) ) {
+                    return TestActivityPubObject::fromArray( $objects[$id] );
+                } else {
+                    return null;
+                }
+            });
+            $objectsService->method( 'update')->willReturnCallback( function( $id, $arr ) {
+                return TestActivityPubObject::fromArray( $arr );
+            });
+            $collectionsService = $this->getMockBuilder( CollectionsService::class )
+                ->disableOriginalConstructor()
+                ->setMethods( array( 'addItem' ) )
+                ->getMock();
+            if ( array_key_exists( 'expectedNewShares', $testCase ) ) {
+                $collectionsService->expects( $this->once() )
+                    ->method( 'addItem' )
+                    ->with(
+                        $this->anything(),
+                        $this->equalTo( $testCase['expectedNewShares'] )
+                    );
+            } else {
+                $collectionsService->expects( $this->never() )
+                    ->method( 'addItem' );
+            }
+            $contextProvider = new ContextProvider();
+            $announceHandler = new AnnounceHandler( $objectsService, $collectionsService, $contextProvider );
+            $eventDispatcher = new EventDispatcher();
+            $eventDispatcher->addSubscriber( $announceHandler );
+            $eventDispatcher->dispatch( $testCase['eventName'], $testCase['event'] );
+        }
+    }
+}
\ No newline at end of file