diff --git a/apps/dav/appinfo/v1/carddav.php b/apps/dav/appinfo/v1/carddav.php
index a47242f825..b8886c0d15 100644
--- a/apps/dav/appinfo/v1/carddav.php
+++ b/apps/dav/appinfo/v1/carddav.php
@@ -27,6 +27,7 @@
  */
 
 // Backends
+use OCA\DAV\AppInfo\PluginManager;
 use OCA\DAV\CardDAV\AddressBookRoot;
 use OCA\DAV\CardDAV\CardDavBackend;
 use OCA\DAV\Connector\LegacyDAVACL;
@@ -34,6 +35,7 @@ use OCA\DAV\Connector\Sabre\Auth;
 use OCA\DAV\Connector\Sabre\ExceptionLoggerPlugin;
 use OCA\DAV\Connector\Sabre\MaintenancePlugin;
 use OCA\DAV\Connector\Sabre\Principal;
+use OCP\App\IAppManager;
 use Sabre\CardDAV\Plugin;
 
 $authBackend = new Auth(
@@ -63,7 +65,8 @@ $debugging = \OC::$server->getConfig()->getSystemValue('debug', false);
 $principalCollection = new \Sabre\CalDAV\Principal\Collection($principalBackend);
 $principalCollection->disableListing = !$debugging; // Disable listing
 
-$addressBookRoot = new AddressBookRoot($principalBackend, $cardDavBackend);
+$pluginManager = new PluginManager(\OC::$server, \OC::$server->query(IAppManager::class));
+$addressBookRoot = new AddressBookRoot($principalBackend, $cardDavBackend, $pluginManager);
 $addressBookRoot->disableListing = !$debugging; // Disable listing
 
 $nodes = array(
diff --git a/apps/dav/composer/composer/autoload_classmap.php b/apps/dav/composer/composer/autoload_classmap.php
index 8a26b80916..ecf51164e8 100644
--- a/apps/dav/composer/composer/autoload_classmap.php
+++ b/apps/dav/composer/composer/autoload_classmap.php
@@ -91,6 +91,8 @@ return array(
     'OCA\\DAV\\CardDAV\\Converter' => $baseDir . '/../lib/CardDAV/Converter.php',
     'OCA\\DAV\\CardDAV\\HasPhotoPlugin' => $baseDir . '/../lib/CardDAV/HasPhotoPlugin.php',
     'OCA\\DAV\\CardDAV\\ImageExportPlugin' => $baseDir . '/../lib/CardDAV/ImageExportPlugin.php',
+    'OCA\\DAV\\CardDAV\\Integration\\ExternalAddressBook' => $baseDir . '/../lib/CardDAV/Integration/ExternalAddressBook.php',
+    'OCA\\DAV\\CardDAV\\Integration\\IAddressBookProvider' => $baseDir . '/../lib/CardDAV/Integration/IAddressBookProvider.php',
     'OCA\\DAV\\CardDAV\\MultiGetExportPlugin' => $baseDir . '/../lib/CardDAV/MultiGetExportPlugin.php',
     'OCA\\DAV\\CardDAV\\PhotoCache' => $baseDir . '/../lib/CardDAV/PhotoCache.php',
     'OCA\\DAV\\CardDAV\\Plugin' => $baseDir . '/../lib/CardDAV/Plugin.php',
diff --git a/apps/dav/composer/composer/autoload_static.php b/apps/dav/composer/composer/autoload_static.php
index 001297ffd2..4df92c174e 100644
--- a/apps/dav/composer/composer/autoload_static.php
+++ b/apps/dav/composer/composer/autoload_static.php
@@ -106,6 +106,8 @@ class ComposerStaticInitDAV
         'OCA\\DAV\\CardDAV\\Converter' => __DIR__ . '/..' . '/../lib/CardDAV/Converter.php',
         'OCA\\DAV\\CardDAV\\HasPhotoPlugin' => __DIR__ . '/..' . '/../lib/CardDAV/HasPhotoPlugin.php',
         'OCA\\DAV\\CardDAV\\ImageExportPlugin' => __DIR__ . '/..' . '/../lib/CardDAV/ImageExportPlugin.php',
+        'OCA\\DAV\\CardDAV\\Integration\\ExternalAddressBook' => __DIR__ . '/..' . '/../lib/CardDAV/Integration/ExternalAddressBook.php',
+        'OCA\\DAV\\CardDAV\\Integration\\IAddressBookProvider' => __DIR__ . '/..' . '/../lib/CardDAV/Integration/IAddressBookProvider.php',
         'OCA\\DAV\\CardDAV\\MultiGetExportPlugin' => __DIR__ . '/..' . '/../lib/CardDAV/MultiGetExportPlugin.php',
         'OCA\\DAV\\CardDAV\\PhotoCache' => __DIR__ . '/..' . '/../lib/CardDAV/PhotoCache.php',
         'OCA\\DAV\\CardDAV\\Plugin' => __DIR__ . '/..' . '/../lib/CardDAV/Plugin.php',
diff --git a/apps/dav/lib/AppInfo/PluginManager.php b/apps/dav/lib/AppInfo/PluginManager.php
index 6a44332ddb..f123648cd3 100644
--- a/apps/dav/lib/AppInfo/PluginManager.php
+++ b/apps/dav/lib/AppInfo/PluginManager.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @copyright Copyright (c) 2016, ownCloud GmbH.
  *
@@ -26,8 +29,12 @@ namespace OCA\DAV\AppInfo;
 
 use OC\ServerContainer;
 use OCA\DAV\CalDAV\Integration\ICalendarProvider;
+use OCA\DAV\CardDAV\Integration\IAddressBookProvider;
 use OCP\App\IAppManager;
 use OCP\AppFramework\QueryException;
+use function array_map;
+use function class_exists;
+use function is_array;
 
 /**
  * Manager for DAV plugins from apps, used to register them
@@ -59,6 +66,13 @@ class PluginManager {
 	 */
 	private $collections = null;
 
+	/**
+	 * Address book plugins
+	 *
+	 * @var IAddressBookProvider[]|null
+	 */
+	private $addressBookPlugins = null;
+
 	/**
 	 * Calendar plugins
 	 *
@@ -101,6 +115,16 @@ class PluginManager {
 		return $this->collections;
 	}
 
+	/**
+	 * @return IAddressBookProvider[]
+	 */
+	public function getAddressBookPlugins(): array {
+		if ($this->addressBookPlugins === null) {
+			$this->populate();
+		}
+		return $this->addressBookPlugins;
+	}
+
 	/**
 	 * Returns an array of app-registered calendar plugins
 	 *
@@ -118,6 +142,7 @@ class PluginManager {
 	 */
 	private function populate() {
 		$this->plugins = [];
+		$this->addressBookPlugins = [];
 		$this->calendarPlugins = [];
 		$this->collections = [];
 		foreach ($this->appManager->getInstalledApps() as $app) {
@@ -128,6 +153,7 @@ class PluginManager {
 			}
 			$this->loadSabrePluginsFromInfoXml($this->extractPluginList($info));
 			$this->loadSabreCollectionsFromInfoXml($this->extractCollectionList($info));
+			$this->loadSabreAddressBookPluginsFromInfoXml($this->extractAddressBookPluginList($info));
 			$this->loadSabreCalendarPluginsFromInfoXml($this->extractCalendarPluginList($info));
 		}
 	}
@@ -162,6 +188,29 @@ class PluginManager {
 		return [];
 	}
 
+	/**
+	 * @param array $array
+	 *
+	 * @return string[]
+	 */
+	private function extractAddressBookPluginList(array $array): array {
+		if (!isset($array['sabre']) || !is_array($array['sabre'])) {
+			return [];
+		}
+		if (!isset($array['sabre']['address-book-plugins']) || !is_array($array['sabre']['address-book-plugins'])) {
+			return [];
+		}
+		if (!isset($array['sabre']['address-book-plugins']['plugin'])) {
+			return [];
+		}
+
+		$items = $array['sabre']['address-book-plugins']['plugin'];
+		if (!is_array($items)) {
+			$items = [$items];
+		}
+		return $items;
+	}
+
 	private function extractCalendarPluginList(array $array):array {
 		if (isset($array['sabre']) && is_array($array['sabre'])) {
 			if (isset($array['sabre']['calendar-plugins']) && is_array($array['sabre']['calendar-plugins'])) {
@@ -205,6 +254,34 @@ class PluginManager {
 		}
 	}
 
+	private function createPluginInstance(string $className) {
+		try {
+			return $this->container->query($className);
+		} catch (QueryException $e) {
+			if (class_exists($className)) {
+				return new $className();
+			}
+		}
+
+		throw new \Exception("Sabre plugin class '$className' is unknown and could not be loaded");
+	}
+
+	/**
+	 * @param string[] $plugin
+	 */
+	private function loadSabreAddressBookPluginsFromInfoXml(array $plugins): void {
+		$providers = array_map(function(string $className): IAddressBookProvider {
+			$instance = $this->createPluginInstance($className);
+			if (!($instance instanceof IAddressBookProvider)) {
+				throw new \Exception("Sabre address book plugin class '$className' does not implement the \OCA\DAV\CardDAV\Integration\IAddressBookProvider interface");
+			}
+			return $instance;
+		}, $plugins);
+		foreach ($providers as $provider) {
+			$this->addressBookPlugins[] = $provider;
+		}
+	}
+
 	private function loadSabreCalendarPluginsFromInfoXml(array $calendarPlugins):void {
 		foreach ($calendarPlugins as $calendarPlugin) {
 			try {
diff --git a/apps/dav/lib/CardDAV/AddressBookRoot.php b/apps/dav/lib/CardDAV/AddressBookRoot.php
index 4b83661679..4436775653 100644
--- a/apps/dav/lib/CardDAV/AddressBookRoot.php
+++ b/apps/dav/lib/CardDAV/AddressBookRoot.php
@@ -24,21 +24,24 @@
 
 namespace OCA\DAV\CardDAV;
 
-use OCP\IL10N;
+use OCA\DAV\AppInfo\PluginManager;
 
 class AddressBookRoot extends \Sabre\CardDAV\AddressBookRoot {
 
-	/** @var IL10N */
-	protected $l10n;
+	/** @var PluginManager */
+	private $pluginManager;
 
 	/**
 	 * @param \Sabre\DAVACL\PrincipalBackend\BackendInterface $principalBackend
 	 * @param \Sabre\CardDAV\Backend\BackendInterface $carddavBackend
 	 * @param string $principalPrefix
 	 */
-	public function __construct(\Sabre\DAVACL\PrincipalBackend\BackendInterface $principalBackend, \Sabre\CardDAV\Backend\BackendInterface $carddavBackend, $principalPrefix = 'principals') {
+	public function __construct(\Sabre\DAVACL\PrincipalBackend\BackendInterface $principalBackend,
+								\Sabre\CardDAV\Backend\BackendInterface $carddavBackend,
+								PluginManager $pluginManager,
+								$principalPrefix = 'principals') {
 		parent::__construct($principalBackend, $carddavBackend, $principalPrefix);
-		$this->l10n = \OC::$server->getL10N('dav');
+		$this->pluginManager = $pluginManager;
 	}
 
 	/**
@@ -49,12 +52,11 @@ class AddressBookRoot extends \Sabre\CardDAV\AddressBookRoot {
 	 * supplied by the authentication backend.
 	 *
 	 * @param array $principal
+	 *
 	 * @return \Sabre\DAV\INode
 	 */
 	function getChildForPrincipal(array $principal) {
-
-		return new UserAddressBooks($this->carddavBackend, $principal['uri'], $this->l10n);
-
+		return new UserAddressBooks($this->carddavBackend, $principal['uri'], $this->pluginManager);
 	}
 
 	function getName() {
diff --git a/apps/dav/lib/CardDAV/Integration/ExternalAddressBook.php b/apps/dav/lib/CardDAV/Integration/ExternalAddressBook.php
new file mode 100644
index 0000000000..6ac36fea44
--- /dev/null
+++ b/apps/dav/lib/CardDAV/Integration/ExternalAddressBook.php
@@ -0,0 +1,113 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\DAV\CardDAV\Integration;
+
+use Sabre\CardDAV\IAddressBook;
+use Sabre\DAV;
+
+/**
+ * @since 19.0.0
+ */
+abstract class ExternalAddressBook implements IAddressBook, DAV\IProperties {
+
+	/** @var string */
+	private const PREFIX = 'app-generated';
+
+	/**
+	 * @var string
+	 *
+	 * Double dash is a valid delimiter,
+	 * because it will always split the URIs correctly:
+	 * - our prefix contains only one dash and won't be split
+	 * - appIds are not allowed to contain dashes as per spec:
+	 * > must contain only lowercase ASCII characters and underscore
+	 * - explode has a limit of three, so even if the app-generated
+	 *   URI has double dashes, it won't be split
+	 */
+	private const DELIMITER = '--';
+
+	/** @var string */
+	private $appId;
+
+	/** @var string */
+	private $uri;
+
+	/**
+	 * @param string $appId
+	 * @param string $uri
+	 */
+	public function __construct(string $appId, string $uri) {
+		$this->appId = $appId;
+		$this->uri = $uri;
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	final public function getName() {
+		return implode(self::DELIMITER, [
+			self::PREFIX,
+			$this->appId,
+			$this->uri,
+		]);
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	final public function setName($name) {
+		throw new DAV\Exception\MethodNotAllowed('Renaming address books is not yet supported');
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	final public function createDirectory($name) {
+		throw new DAV\Exception\MethodNotAllowed('Creating collections in address book objects is not allowed');
+
+	}
+
+	/**
+	 * Checks whether the address book uri is app-generated
+	 *
+	 * @param string $uri
+	 *
+	 * @return bool
+	 */
+	public static function isAppGeneratedAddressBook(string $uri): bool {
+		return strpos($uri, self::PREFIX) === 0 && substr_count($uri, self::DELIMITER) >= 2;
+	}
+
+	/**
+	 * Splits an app-generated uri into appId and uri
+	 *
+	 * @param string $uri
+	 *
+	 * @return array
+	 */
+	public static function splitAppGeneratedAddressBookUri(string $uri): array {
+		$array = array_slice(explode(self::DELIMITER, $uri, 3), 1);
+		// Check the array has expected amount of elements
+		// and none of them is an empty string
+		if (\count($array) !== 2 || \in_array('', $array, true)) {
+			throw new \InvalidArgumentException('Provided address book uri was not app-generated');
+		}
+
+		return $array;
+	}
+
+	/**
+	 * Checks whether a address book name the user wants to create violates
+	 * the reserved name for URIs
+	 *
+	 * @param string $uri
+	 *
+	 * @return bool
+	 */
+	public static function doesViolateReservedName(string $uri): bool {
+		return strpos($uri, self::PREFIX) === 0;
+	}
+
+}
diff --git a/apps/dav/lib/CardDAV/Integration/IAddressBookProvider.php b/apps/dav/lib/CardDAV/Integration/IAddressBookProvider.php
new file mode 100644
index 0000000000..4410a7486b
--- /dev/null
+++ b/apps/dav/lib/CardDAV/Integration/IAddressBookProvider.php
@@ -0,0 +1,53 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\DAV\CardDAV\Integration;
+
+use Sabre\CardDAV\IAddressBook;
+
+/**
+ * @since 19.0.0
+ */
+interface IAddressBookProvider {
+
+	/**
+	 * Provides the appId of the plugin
+	 *
+	 * @since 19.0.0
+	 * @return string AppId
+	 */
+	public function getAppId(): string;
+
+	/**
+	 * Fetches all address books for a given principal uri
+	 *
+	 * @since 19.0.0
+	 * @param string $principalUri E.g. principals/users/user1
+	 * @return ExternalAddressBook[] Array of all address books
+	 */
+	public function fetchAllForAddressBookHome(string $principalUri): array;
+
+	/**
+	 * Checks whether plugin has an address book for a given principalUri and URI
+	 *
+	 * @since 19.0.0
+	 * @param string $principalUri E.g. principals/users/user1
+	 * @param string $uri E.g. personal
+	 * @return bool True if address book for principalUri and URI exists, false otherwise
+	 */
+	public function hasAddressBookInAddressBookHome(string $principalUri, string $uri): bool;
+
+	/**
+	 * Fetches an address book for a given principalUri and URI
+	 * Returns null if address book does not exist
+	 *
+	 * @param string $principalUri E.g. principals/users/user1
+	 * @param string $uri E.g. personal
+	 *
+	 * @return ExternalAddressBook|null address book if it exists, null otherwise
+	 *@since 19.0.0
+	 */
+	public function getAddressBookInAddressBookHome(string $principalUri, string $uri): ?ExternalAddressBook;
+
+}
diff --git a/apps/dav/lib/CardDAV/UserAddressBooks.php b/apps/dav/lib/CardDAV/UserAddressBooks.php
index 3ba20cfffa..8b9e22db5a 100644
--- a/apps/dav/lib/CardDAV/UserAddressBooks.php
+++ b/apps/dav/lib/CardDAV/UserAddressBooks.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @copyright Copyright (c) 2016, ownCloud, Inc.
  *
@@ -24,8 +27,13 @@
 
 namespace OCA\DAV\CardDAV;
 
+use OCA\DAV\AppInfo\PluginManager;
+use OCA\DAV\CardDAV\Integration\ExternalAddressBook;
 use OCP\IConfig;
 use OCP\IL10N;
+use Sabre\CardDAV\Backend;
+use Sabre\DAV\Exception\MethodNotAllowed;
+use Sabre\DAV\MkCol;
 
 class UserAddressBooks extends \Sabre\CardDAV\AddressBookHome {
 
@@ -35,8 +43,18 @@ class UserAddressBooks extends \Sabre\CardDAV\AddressBookHome {
 	/** @var IConfig */
 	protected $config;
 
+	/** @var PluginManager */
+	private $pluginManager;
+
+	public function __construct(Backend\BackendInterface $carddavBackend,
+								string $principalUri,
+								PluginManager $pluginManager) {
+		parent::__construct($carddavBackend, $principalUri);
+		$this->pluginManager = $pluginManager;
+	}
+
 	/**
-	 * Returns a list of addressbooks
+	 * Returns a list of address books
 	 *
 	 * @return array
 	 */
@@ -49,18 +67,28 @@ class UserAddressBooks extends \Sabre\CardDAV\AddressBookHome {
 		}
 
 		$addressBooks = $this->carddavBackend->getAddressBooksForUser($this->principalUri);
-		$objects = [];
-		foreach($addressBooks as $addressBook) {
+		$objects = array_map(function(array $addressBook) {
 			if ($addressBook['principaluri'] === 'principals/system/system') {
-				$objects[] = new SystemAddressbook($this->carddavBackend, $addressBook, $this->l10n, $this->config);
-			} else {
-				$objects[] = new AddressBook($this->carddavBackend, $addressBook, $this->l10n);
+				return new SystemAddressbook($this->carddavBackend, $addressBook, $this->l10n, $this->config);
 			}
+
+			return new AddressBook($this->carddavBackend, $addressBook, $this->l10n);
+		}, $addressBooks);
+		foreach ($this->pluginManager->getAddressBookPlugins() as $plugin) {
+			$plugin->fetchAllForAddressBookHome($this->principalUri);
 		}
 		return $objects;
 
 	}
 
+	public function createExtendedCollection($name, MkCol $mkCol) {
+		if (ExternalAddressBook::doesViolateReservedName($name)) {
+			throw new MethodNotAllowed('The resource you tried to create has a reserved name');
+		}
+
+		parent::createExtendedCollection($name, $mkCol);
+	}
+
 	/**
 	 * Returns a list of ACE's for this node.
 	 *
@@ -78,9 +106,9 @@ class UserAddressBooks extends \Sabre\CardDAV\AddressBookHome {
 		$acl = parent::getACL();
 		if ($this->principalUri === 'principals/system/system') {
 			$acl[] = [
-					'privilege' => '{DAV:}read',
-					'principal' => '{DAV:}authenticated',
-					'protected' => true,
+				'privilege' => '{DAV:}read',
+				'principal' => '{DAV:}authenticated',
+				'protected' => true,
 			];
 		}
 
diff --git a/apps/dav/lib/RootCollection.php b/apps/dav/lib/RootCollection.php
index becbbb3847..6f8e74692c 100644
--- a/apps/dav/lib/RootCollection.php
+++ b/apps/dav/lib/RootCollection.php
@@ -27,6 +27,7 @@
 
 namespace OCA\DAV;
 
+use OCA\DAV\AppInfo\PluginManager;
 use OCA\DAV\CalDAV\CalDavBackend;
 use OCA\DAV\CalDAV\CalendarRoot;
 use OCA\DAV\CalDAV\Principal\Collection;
@@ -41,6 +42,7 @@ use OCA\DAV\DAV\GroupPrincipalBackend;
 use OCA\DAV\DAV\SystemPrincipalBackend;
 use OCA\DAV\Provisioning\Apple\AppleProvisioningNode;
 use OCA\DAV\Upload\CleanupService;
+use OCP\App\IAppManager;
 use OCP\AppFramework\Utility\ITimeFactory;
 use Sabre\DAV\SimpleCollection;
 
@@ -123,12 +125,13 @@ class RootCollection extends SimpleCollection {
 			\OC::$server->getLogger()
 		);
 
+		$pluginManager = new PluginManager(\OC::$server, \OC::$server->query(IAppManager::class));
 		$usersCardDavBackend = new CardDavBackend($db, $userPrincipalBackend, $userManager, $groupManager, $dispatcher);
-		$usersAddressBookRoot = new AddressBookRoot($userPrincipalBackend, $usersCardDavBackend, 'principals/users');
+		$usersAddressBookRoot = new AddressBookRoot($userPrincipalBackend, $usersCardDavBackend, $pluginManager, 'principals/users');
 		$usersAddressBookRoot->disableListing = $disableListing;
 
 		$systemCardDavBackend = new CardDavBackend($db, $userPrincipalBackend, $userManager, $groupManager, $dispatcher);
-		$systemAddressBookRoot = new AddressBookRoot(new SystemPrincipalBackend(), $systemCardDavBackend, 'principals/system');
+		$systemAddressBookRoot = new AddressBookRoot(new SystemPrincipalBackend(), $systemCardDavBackend, $pluginManager, 'principals/system');
 		$systemAddressBookRoot->disableListing = $disableListing;
 
 		$uploadCollection = new Upload\RootCollection(