diff --git a/lib/public/systemtag/isystemtag.php b/lib/public/systemtag/isystemtag.php
new file mode 100644
index 0000000000000000000000000000000000000000..76a812f38dc7c8c33cd2f6833ee150c4b19a69d6
--- /dev/null
+++ b/lib/public/systemtag/isystemtag.php
@@ -0,0 +1,68 @@
+<?php
+/**
+ * @author Vincent Petry <pvince81@owncloud.com>
+ *
+ * @copyright Copyright (c) 2015, ownCloud, Inc.
+ * @license AGPL-3.0
+ *
+ * This code is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License, version 3,
+ * along with this program. If not, see <http://www.gnu.org/licenses/>
+ *
+ */
+
+namespace OCP\SystemTag;
+
+/**
+ * Public interface for a system-wide tag.
+ *
+ * @since 9.0.0
+ */
+interface ISystemTag {
+
+ /**
+ * Returns the tag id
+ *
+ * @return string id
+ *
+ * @since 9.0.0
+ */
+ public function getId();
+
+ /**
+ * Returns the tag display name
+ *
+ * @return string tag display name
+ *
+ * @since 9.0.0
+ */
+ public function getName();
+
+ /**
+ * Returns whether the tag is visible for regular users
+ *
+ * @return bool true if visible, false otherwise
+ *
+ * @since 9.0.0
+ */
+ public function isUserVisible();
+
+ /**
+ * Returns whether the tag can be assigned to objects by regular users
+ *
+ * @return bool true if assignable, false otherwise
+ *
+ * @since 9.0.0
+ */
+ public function isUserAsssignable();
+
+}
+
diff --git a/lib/public/systemtag/isystemtagobjectmapper.php b/lib/public/systemtag/isystemtagobjectmapper.php
new file mode 100644
index 0000000000000000000000000000000000000000..87f3fd0473f61e6fff06677b5c2ead518cfebc88
--- /dev/null
+++ b/lib/public/systemtag/isystemtagobjectmapper.php
@@ -0,0 +1,115 @@
+<?php
+/**
+ * @author Vincent Petry <pvince81@owncloud.com>
+ *
+ * @copyright Copyright (c) 2015, ownCloud, Inc.
+ * @license AGPL-3.0
+ *
+ * This code is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License, version 3,
+ * along with this program. If not, see <http://www.gnu.org/licenses/>
+ *
+ */
+
+namespace OCP\SystemTag;
+
+/**
+ * Public interface to access and manage system-wide tags.
+ *
+ * @since 9.0.0
+ */
+interface ISystemTagObjectMapper {
+
+ /**
+ * Get a list of tag ids for the given object ids.
+ *
+ * This returns an array that maps object id to tag ids
+ * [
+ * 1 => array('id1', 'id2'),
+ * 2 => array('id3', 'id2'),
+ * 3 => array('id5'),
+ * 4 => array()
+ * ]
+ *
+ * Untagged objects will have an empty array associated.
+ *
+ * @param string|array $objIds object ids
+ * @param string $objectType object type
+ *
+ * @return array with object id as key and an array
+ * of tag ids as value
+ *
+ * @since 9.0.0
+ */
+ public function getTagIdsForObjects($objIds, $objectType);
+
+ /**
+ * Get a list of objects tagged with $tagIds.
+ *
+ * @param string|array $tagIds Tag id or array of tag ids.
+ * @param string $objectType object type
+ *
+ * @return string[] array of object ids or empty array if none found
+ *
+ * @throws \OCP\SystemTag\TagNotFoundException if at least one of the
+ * given tags does not exist
+ *
+ * @since 9.0.0
+ */
+ public function getObjectIdsForTags($tagIds, $objectType);
+
+ /**
+ * Assign the given tags to the given object.
+ *
+ * @param string $objId object id
+ * @param string $objectType object type
+ * @param string|array $tagIds tag id or array of tag ids to assign
+ *
+ * @throws \OCP\SystemTag\TagNotFoundException if at least one of the
+ * given tags does not exist
+ *
+ * @since 9.0.0
+ */
+ public function assignTags($objId, $objectType, $tagIds);
+
+ /**
+ * Unassign the given tags from the given object.
+ *
+ * @param string $objId object id
+ * @param string $objectType object type
+ * @param string|array $tagIds tag id or array of tag ids to unassign
+ *
+ * @throws \OCP\SystemTag\TagNotFoundException if at least one of the
+ * given tags does not exist
+ *
+ * @since 9.0.0
+ */
+ public function unassignTags($objId, $objectType, $tagIds);
+
+ /**
+ * Checks whether the given objects have the given tag.
+ *
+ * @param string|array $objIds object ids
+ * @param string $objectType object type
+ * @param string $tagId tag id to check
+ * @param bool $all true to check that ALL objects have the tag assigned,
+ * false to check that at least ONE object has the tag.
+ *
+ * @return bool true if the condition set by $all is matched, false
+ * otherwise
+ *
+ * @throws \OCP\SystemTag\TagNotFoundException if the tag does not exist
+ *
+ * @since 9.0.0
+ */
+ public function hasTags($objIds, $objectType, $tagId, $all = true);
+
+}
diff --git a/lib/public/systemtag/isystemtagsmanager.php b/lib/public/systemtag/isystemtagsmanager.php
new file mode 100644
index 0000000000000000000000000000000000000000..df59cc48d52e72977c226374b5acd2c7c3a7929f
--- /dev/null
+++ b/lib/public/systemtag/isystemtagsmanager.php
@@ -0,0 +1,111 @@
+<?php
+/**
+ * @author Vincent Petry <pvince81@owncloud.com>
+ *
+ * @copyright Copyright (c) 2015, ownCloud, Inc.
+ * @license AGPL-3.0
+ *
+ * This code is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License, version 3,
+ * along with this program. If not, see <http://www.gnu.org/licenses/>
+ *
+ */
+
+namespace OCP\SystemTag;
+
+/**
+ * Public interface to access and manage system-wide tags.
+ *
+ * @since 9.0.0
+ */
+interface ISystemTagManager {
+
+ /**
+ * Returns the tag objects matching the given tag ids.
+ *
+ * @param array|string $tagIds The ID or array of IDs of the tags to retrieve
+ *
+ * @return \OCP\SystemTag\ISystemTag[] array of system tags or empty array if none found
+ *
+ * @since 9.0.0
+ */
+ public function getTagsById($tagIds);
+
+ /**
+ * Returns the tag object matching the given attributes.
+ *
+ * @param string $tagName tag name
+ * @param bool $userVisible whether the tag is visible by users
+ * @param bool $userAssignable whether the tag is assignable by users
+ *
+ * @return \OCP\SystemTag\ISystemTag system tag
+ *
+ * @throws \OCP\SystemTag\TagNotFoundException if tag does not exist
+ *
+ * @since 9.0.0
+ */
+ public function getTag($tagName, $userVisible, $userAssignable);
+
+ /**
+ * Creates the tag object using the given attributes.
+ *
+ * @param string $tagName tag name
+ * @param bool $userVisible whether the tag is visible by users
+ * @param bool $userAssignable whether the tag is assignable by users
+ *
+ * @return \OCP\SystemTag\ISystemTag system tag
+ *
+ * @throws \OCP\SystemTag\TagAlreadyExistsException if tag already exists
+ *
+ * @since 9.0.0
+ */
+ public function createTag($tagName, $userVisible, $userAssignable);
+
+ /**
+ * Returns all known tags, optionally filtered by visibility.
+ *
+ * @param bool $visibleOnly whether to only return user visible tags
+ * @param string $nameSearchPattern optional search pattern for the tag name
+ *
+ * @return \OCP\SystemTag\ISystemTag[] array of system tags or empty array if none found
+ *
+ * @since 9.0.0
+ */
+ public function getAllTags($visibleOnly = false, $nameSearchPattern = null);
+
+ /**
+ * Updates the given tag
+ *
+ * @param string $tagId tag id
+ * @param string $newName the new tag name
+ * @param bool $userVisible whether the tag is visible by users
+ * @param bool $userAssignable whether the tag is assignable by users
+ *
+ * @throws \OCP\SystemTag\TagNotFoundException if tag with the given id does not exist
+ * @throws \OCP\SystemTag\TagAlreadyExistsException if there is already another tag
+ * with the same attributes
+ *
+ * @since 9.0.0
+ */
+ public function updateTag($tagId, $newName, $userVisible, $userAssignable);
+
+ /**
+ * Delete the given tags from the database and all their relationships.
+ *
+ * @param string|array $tagIds array of tag ids
+ *
+ * @throws \OCP\SystemTag\TagNotFoundException if tag did not exist
+ *
+ * @since 9.0.0
+ */
+ public function deleteTags($tagIds);
+
+}
diff --git a/lib/public/systemtag/tagalreadyexistsexception.php b/lib/public/systemtag/tagalreadyexistsexception.php
new file mode 100644
index 0000000000000000000000000000000000000000..d192b38e7bc5ee059c754b5abbaa17fae8dece0a
--- /dev/null
+++ b/lib/public/systemtag/tagalreadyexistsexception.php
@@ -0,0 +1,29 @@
+<?php
+/**
+ * @author Vincent Petry <pvince81@owncloud.com>
+ *
+ * @copyright Copyright (c) 2015, ownCloud, Inc.
+ * @license AGPL-3.0
+ *
+ * This code is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License, version 3,
+ * along with this program. If not, see <http://www.gnu.org/licenses/>
+ *
+ */
+
+namespace OCP\SystemTag;
+
+/**
+ * Exception when a tag already exists.
+ *
+ * @since 9.0.0
+ */
+class TagAlreadyExistsException extends \RuntimeException {}
diff --git a/lib/public/systemtag/tagnotfoundexception.php b/lib/public/systemtag/tagnotfoundexception.php
new file mode 100644
index 0000000000000000000000000000000000000000..94bb07c8c12c979328eee0085e1813d161702f1d
--- /dev/null
+++ b/lib/public/systemtag/tagnotfoundexception.php
@@ -0,0 +1,29 @@
+<?php
+/**
+ * @author Vincent Petry <pvince81@owncloud.com>
+ *
+ * @copyright Copyright (c) 2015, ownCloud, Inc.
+ * @license AGPL-3.0
+ *
+ * This code is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License, version 3,
+ * along with this program. If not, see <http://www.gnu.org/licenses/>
+ *
+ */
+
+namespace OCP\SystemTag;
+
+/**
+ * Exception when a tag was not found.
+ *
+ * @since 9.0.0
+ */
+class TagNotFoundException extends \RuntimeException {}