diff --git a/apps/dav/appinfo/application.php b/apps/dav/appinfo/application.php
index d06daf97f5..593cd770be 100644
--- a/apps/dav/appinfo/application.php
+++ b/apps/dav/appinfo/application.php
@@ -27,6 +27,8 @@ use OCA\DAV\CardDAV\CardDavBackend;
 use OCA\DAV\CardDAV\ContactsManager;
 use OCA\DAV\CardDAV\SyncJob;
 use OCA\DAV\CardDAV\SyncService;
+use OCA\DAV\Connector\Sabre\Principal;
+use OCA\DAV\DAV\GroupPrincipalBackend;
 use OCA\DAV\HookManager;
 use OCA\Dav\Migration\AddressBookAdapter;
 use OCA\Dav\Migration\CalendarAdapter;
@@ -79,7 +81,7 @@ class Application extends App {
 			/** @var IAppContainer $c */
 			$db = $c->getServer()->getDatabaseConnection();
 			$dispatcher = $c->getServer()->getEventDispatcher();
-			$principal = new \OCA\DAV\Connector\Sabre\Principal(
+			$principal = new Principal(
 				$c->getServer()->getUserManager(),
 				$c->getServer()->getGroupManager()
 			);
@@ -89,7 +91,7 @@ class Application extends App {
 		$container->registerService('CalDavBackend', function($c) {
 			/** @var IAppContainer $c */
 			$db = $c->getServer()->getDatabaseConnection();
-			$principal = new \OCA\DAV\Connector\Sabre\Principal(
+			$principal = new Principal(
 				$c->getServer()->getUserManager(),
 				$c->getServer()->getGroupManager()
 			);
@@ -122,11 +124,14 @@ class Application extends App {
 
 		$container->registerService('BirthdayService', function($c) {
 			/** @var IAppContainer $c */
+			$g = new GroupPrincipalBackend(
+				$c->getServer()->getGroupManager()
+			);
 			return new BirthdayService(
 				$c->query('CalDavBackend'),
-				$c->query('CardDavBackend')
+				$c->query('CardDavBackend'),
+				$g
 			);
-
 		});
 	}
 
@@ -147,6 +152,7 @@ class Application extends App {
 
 		$listener = function($event) {
 			if ($event instanceof GenericEvent) {
+				/** @var BirthdayService $b */
 				$b = $this->getContainer()->query('BirthdayService');
 				$b->onCardChanged(
 					$event->getArgument('addressBookId'),
@@ -161,6 +167,7 @@ class Application extends App {
 		$dispatcher->addListener('\OCA\DAV\CardDAV\CardDavBackend::updateCard', $listener);
 		$dispatcher->addListener('\OCA\DAV\CardDAV\CardDavBackend::deleteCard', function($event) {
 			if ($event instanceof GenericEvent) {
+				/** @var BirthdayService $b */
 				$b = $this->getContainer()->query('BirthdayService');
 				$b->onCardDeleted(
 					$event->getArgument('addressBookId'),
diff --git a/apps/dav/lib/caldav/birthdayservice.php b/apps/dav/lib/caldav/birthdayservice.php
index e03a630fed..1d0b06f03a 100644
--- a/apps/dav/lib/caldav/birthdayservice.php
+++ b/apps/dav/lib/caldav/birthdayservice.php
@@ -23,6 +23,7 @@ namespace OCA\DAV\CalDAV;
 
 use Exception;
 use OCA\DAV\CardDAV\CardDavBackend;
+use OCA\DAV\DAV\GroupPrincipalBackend;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\Reader;
 
@@ -30,15 +31,20 @@ class BirthdayService {
 
 	const BIRTHDAY_CALENDAR_URI = 'contact_birthdays';
 
+	/** @var GroupPrincipalBackend */
+	private $principalBackend;
+
 	/**
 	 * BirthdayService constructor.
 	 *
 	 * @param CalDavBackend $calDavBackEnd
 	 * @param CardDavBackend $cardDavBackEnd
+	 * @param GroupPrincipalBackend $principalBackend
 	 */
-	public function __construct($calDavBackEnd, $cardDavBackEnd) {
+	public function __construct($calDavBackEnd, $cardDavBackEnd, $principalBackend) {
 		$this->calDavBackEnd = $calDavBackEnd;
 		$this->cardDavBackEnd = $cardDavBackEnd;
+		$this->principalBackend = $principalBackend;
 	}
 
 	/**
@@ -48,22 +54,26 @@ class BirthdayService {
 	 */
 	public function onCardChanged($addressBookId, $cardUri, $cardData) {
 
+		$targetPrincipals = $this->getAllAffectedPrincipals($addressBookId);
+		
 		$book = $this->cardDavBackEnd->getAddressBookById($addressBookId);
-		$principalUri = $book['principaluri'];
-		$calendar = $this->ensureCalendarExists($principalUri);
-		$objectUri = $book['uri'] . '-' . $cardUri. '.ics';
-		$calendarData = $this->buildBirthdayFromContact($cardData);
-		$existing = $this->calDavBackEnd->getCalendarObject($calendar['id'], $objectUri);
-		if (is_null($calendarData)) {
-			if (!is_null($existing)) {
-				$this->calDavBackEnd->deleteCalendarObject($calendar['id'], $objectUri);
-			}
-		} else {
-			if (is_null($existing)) {
-				$this->calDavBackEnd->createCalendarObject($calendar['id'], $objectUri, $calendarData->serialize());
+		$targetPrincipals[] = $book['principaluri'];
+		foreach ($targetPrincipals as $principalUri) {
+			$calendar = $this->ensureCalendarExists($principalUri);
+			$objectUri = $book['uri'] . '-' . $cardUri. '.ics';
+			$calendarData = $this->buildBirthdayFromContact($cardData);
+			$existing = $this->calDavBackEnd->getCalendarObject($calendar['id'], $objectUri);
+			if (is_null($calendarData)) {
+				if (!is_null($existing)) {
+					$this->calDavBackEnd->deleteCalendarObject($calendar['id'], $objectUri);
+				}
 			} else {
-				if ($this->birthdayEvenChanged($existing['calendardata'], $calendarData)) {
-					$this->calDavBackEnd->updateCalendarObject($calendar['id'], $objectUri, $calendarData->serialize());
+				if (is_null($existing)) {
+					$this->calDavBackEnd->createCalendarObject($calendar['id'], $objectUri, $calendarData->serialize());
+				} else {
+					if ($this->birthdayEvenChanged($existing['calendardata'], $calendarData)) {
+						$this->calDavBackEnd->updateCalendarObject($calendar['id'], $objectUri, $calendarData->serialize());
+					}
 				}
 			}
 		}
@@ -74,11 +84,14 @@ class BirthdayService {
 	 * @param string $cardUri
 	 */
 	public function onCardDeleted($addressBookId, $cardUri) {
+		$targetPrincipals = $this->getAllAffectedPrincipals($addressBookId);
 		$book = $this->cardDavBackEnd->getAddressBookById($addressBookId);
-		$principalUri = $book['principaluri'];
-		$calendar = $this->ensureCalendarExists($principalUri);
-		$objectUri = $book['uri'] . '-' . $cardUri. '.ics';
-		$this->calDavBackEnd->deleteCalendarObject($calendar['id'], $objectUri);
+		$targetPrincipals[] = $book['principaluri'];
+		foreach ($targetPrincipals as $principalUri) {
+			$calendar = $this->ensureCalendarExists($principalUri);
+			$objectUri = $book['uri'] . '-' . $cardUri . '.ics';
+			$this->calDavBackEnd->deleteCalendarObject($calendar['id'], $objectUri);
+		}
 	}
 
 	/**
@@ -190,4 +203,24 @@ class BirthdayService {
 		return false;
 	}
 
+	/**
+	 * @param $addressBookId
+	 * @return mixed
+	 */
+	protected function getAllAffectedPrincipals($addressBookId) {
+		$targetPrincipals = [];
+		$shares = $this->cardDavBackEnd->getShares($addressBookId);
+		foreach ($shares as $share) {
+			if ($share['{http://owncloud.org/ns}group-share']) {
+				$users = $this->principalBackend->getGroupMemberSet($share['{http://owncloud.org/ns}principal']);
+				foreach ($users as $user) {
+					$targetPrincipals[] = $user['uri'];
+				}
+			} else {
+				$targetPrincipals[] = $share['{http://owncloud.org/ns}principal'];
+			}
+		}
+		return array_values(array_unique($targetPrincipals, SORT_STRING));
+	}
+
 }
diff --git a/apps/dav/lib/dav/groupprincipalbackend.php b/apps/dav/lib/dav/groupprincipalbackend.php
index 34c00b7927..e056863978 100644
--- a/apps/dav/lib/dav/groupprincipalbackend.php
+++ b/apps/dav/lib/dav/groupprincipalbackend.php
@@ -22,6 +22,7 @@ namespace OCA\DAV\DAV;
 
 use OCP\IGroup;
 use OCP\IGroupManager;
+use OCP\IUser;
 use Sabre\DAV\Exception;
 use \Sabre\DAV\PropPatch;
 use Sabre\DAVACL\PrincipalBackend\BackendInterface;
@@ -82,10 +83,10 @@ class GroupPrincipalBackend implements BackendInterface {
 			return null;
 		}
 		$name = $elements[2];
-		$user = $this->groupManager->get($name);
+		$group = $this->groupManager->get($name);
 
-		if (!is_null($user)) {
-			return $this->groupToPrincipal($user);
+		if (!is_null($group)) {
+			return $this->groupToPrincipal($group);
 		}
 
 		return null;
@@ -99,8 +100,23 @@ class GroupPrincipalBackend implements BackendInterface {
 	 * @throws Exception
 	 */
 	public function getGroupMemberSet($principal) {
-		// TODO: implement if we want that
-		return [];
+		$elements = explode('/', $principal);
+		if ($elements[0] !== 'principals') {
+			return [];
+		}
+		if ($elements[1] !== 'groups') {
+			return [];
+		}
+		$name = $elements[2];
+		$group = $this->groupManager->get($name);
+
+		if (is_null($group)) {
+			return [];
+		}
+
+		return array_map(function($user) {
+			return $this->userToPrincipal($user);
+		}, $group->getUsers());
 	}
 
 	/**
@@ -162,8 +178,21 @@ class GroupPrincipalBackend implements BackendInterface {
 	protected function groupToPrincipal($group) {
 		$groupId = $group->getGID();
 		$principal = [
-				'uri' => "principals/groups/$groupId",
-				'{DAV:}displayname' => $groupId,
+			'uri' => "principals/groups/$groupId",
+			'{DAV:}displayname' => $groupId,
+		];
+
+		return $principal;
+	}
+
+	/**
+	 * @param IUser $user
+	 * @return array
+	 */
+	protected function userToPrincipal($user) {
+		$principal = [
+			'uri' => 'principals/users/' . $user->getUID(),
+			'{DAV:}displayname' => $user->getDisplayName(),
 		];
 
 		return $principal;
diff --git a/apps/dav/lib/dav/sharing/backend.php b/apps/dav/lib/dav/sharing/backend.php
index ffc4193e34..225b773713 100644
--- a/apps/dav/lib/dav/sharing/backend.php
+++ b/apps/dav/lib/dav/sharing/backend.php
@@ -161,7 +161,8 @@ class Backend {
 				'commonName' => isset($p['{DAV:}displayname']) ? $p['{DAV:}displayname'] : '',
 				'status' => 1,
 				'readOnly' => ($row['access'] == self::ACCESS_READ),
-				'{'.\OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD.'}principal' => $row['principaluri']
+				'{http://owncloud.org/ns}principal' => $row['principaluri'],
+				'{http://owncloud.org/ns}group-share' => is_null($p)
 			];
 		}
 
diff --git a/apps/dav/tests/unit/carddav/birthdayservicetest.php b/apps/dav/tests/unit/carddav/birthdayservicetest.php
index 2efb3c09ae..e15edd16c6 100644
--- a/apps/dav/tests/unit/carddav/birthdayservicetest.php
+++ b/apps/dav/tests/unit/carddav/birthdayservicetest.php
@@ -24,6 +24,7 @@ namespace OCA\DAV\Tests\Unit\CardDAV;
 use OCA\DAV\CalDAV\BirthdayService;
 use OCA\DAV\CalDAV\CalDavBackend;
 use OCA\DAV\CardDAV\CardDavBackend;
+use OCA\DAV\DAV\GroupPrincipalBackend;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\Reader;
 use Test\TestCase;
@@ -36,14 +37,17 @@ class BirthdayServiceTest extends TestCase {
 	private $calDav;
 	/** @var CardDavBackend | \PHPUnit_Framework_MockObject_MockObject */
 	private $cardDav;
+	/** @var GroupPrincipalBackend | \PHPUnit_Framework_MockObject_MockObject */
+	private $groupPrincialBackend;
 
 	public function setUp() {
 		parent::setUp();
 
 		$this->calDav = $this->getMockBuilder('OCA\DAV\CalDAV\CalDavBackend')->disableOriginalConstructor()->getMock();
 		$this->cardDav = $this->getMockBuilder('OCA\DAV\CardDAV\CardDavBackend')->disableOriginalConstructor()->getMock();
+		$this->groupPrincialBackend = $this->getMockBuilder('OCA\DAV\DAV\GroupPrincipalBackend')->disableOriginalConstructor()->getMock();
 
-		$this->service = new BirthdayService($this->calDav, $this->cardDav);
+		$this->service = new BirthdayService($this->calDav, $this->cardDav, $this->groupPrincialBackend);
 	}
 
 	/**
@@ -77,6 +81,7 @@ class BirthdayServiceTest extends TestCase {
 			'id' => 1234
 		]);
 		$this->calDav->expects($this->once())->method('deleteCalendarObject')->with(1234, 'default-gump.vcf.ics');
+		$this->cardDav->expects($this->once())->method('getShares')->willReturn([]);
 
 		$this->service->onCardDeleted(666, 'gump.vcf');
 	}
@@ -96,10 +101,11 @@ class BirthdayServiceTest extends TestCase {
 			->willReturn([
 				'id' => 1234
 			]);
+		$this->cardDav->expects($this->once())->method('getShares')->willReturn([]);
 
 		/** @var BirthdayService | \PHPUnit_Framework_MockObject_MockObject $service */
 		$service = $this->getMock('\OCA\DAV\CalDAV\BirthdayService',
-			['buildBirthdayFromContact', 'birthdayEvenChanged'], [$this->calDav, $this->cardDav]);
+			['buildBirthdayFromContact', 'birthdayEvenChanged'], [$this->calDav, $this->cardDav, $this->groupPrincialBackend]);
 
 		if ($expectedOp === 'delete') {
 			$this->calDav->expects($this->once())->method('getCalendarObject')->willReturn('');
@@ -132,6 +138,45 @@ class BirthdayServiceTest extends TestCase {
 		$this->assertEquals($expected, $this->service->birthdayEvenChanged($old, $new));
 	}
 
+	public function testGetAllAffectedPrincipals() {
+		$this->cardDav->expects($this->once())->method('getShares')->willReturn([
+			[
+				'{http://owncloud.org/ns}group-share' => false,
+				'{http://owncloud.org/ns}principal' => 'principals/users/user01'
+			],
+			[
+				'{http://owncloud.org/ns}group-share' => false,
+				'{http://owncloud.org/ns}principal' => 'principals/users/user01'
+			],
+			[
+				'{http://owncloud.org/ns}group-share' => false,
+				'{http://owncloud.org/ns}principal' => 'principals/users/user02'
+			],
+			[
+				'{http://owncloud.org/ns}group-share' => true,
+				'{http://owncloud.org/ns}principal' => 'principals/groups/users'
+			],
+		]);
+		$this->groupPrincialBackend->expects($this->once())->method('getGroupMemberSet')
+			->willReturn([
+				[
+					'uri' => 'principals/users/user01',
+				],
+				[
+					'uri' => 'principals/users/user02',
+				],
+				[
+					'uri' => 'principals/users/user03',
+				],
+			]);
+		$users = $this->invokePrivate($this->service, 'getAllAffectedPrincipals', [6666]);
+		$this->assertEquals([
+			'principals/users/user01',
+			'principals/users/user02',
+			'principals/users/user03'
+		], $users);
+	}
+
 	public function providesBirthday() {
 		return [
 			[true,