diff --git a/calendarserver.php b/calendarserver.php
--- a/calendarserver.php
+++ b/calendarserver.php
@@ -1,97 +1,96 @@
 <?php
 
 if(!defined('DOKU_INC')) define('DOKU_INC', dirname(__FILE__).'/../../../');
 if (!defined('DOKU_DISABLE_GZIP_OUTPUT')) define('DOKU_DISABLE_GZIP_OUTPUT', 1);
 require_once(DOKU_INC.'inc/init.php');
 session_write_close(); //close session
 
 require_once (DOKU_INC.'inc/fetch.functions.php');
 
 global $conf;
 
 $baseUri = DOKU_BASE.'lib/plugins/davcal/'.basename(__FILE__).'/';
 $sqlFile = $conf['metadir'].'/davcal.sqlite3';
 
 if(!file_exists($sqlFile))
 {
     die('SQL File doesn\'t exist');
 }
 
 /*
 
 CalendarServer example
 
 This server features CalDAV support
 
 */
 
 // settings
 // date_default_timezone_set('Canada/Eastern');
 
 // If you want to run the SabreDAV server in a custom location (using mod_rewrite for instance)
 // You can override the baseUri here.
 // $baseUri = '/';
 
 /* Database */
 $pdo = new PDO('sqlite:'.$sqlFile);
 $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
 
 //Mapping PHP errors to exceptions
 function exception_error_handler($errno, $errstr, $errfile, $errline) {
     throw new ErrorException($errstr, 0, $errno, $errfile, $errline);
 }
 //set_error_handler("exception_error_handler");
 
 // Files we need
 require_once 'vendor/autoload.php';
 require_once('authBackendDokuwiki.php');
 require_once('principalBackendDokuwiki.php');
 require_once('calendarBackendDokuwiki.php');
 
 // Backends
 $authBackend = new DokuWikiSabreAuthBackend();
 $calendarBackend = new DokuWikiSabreCalendarBackend($pdo); //Sabre\CalDAV\Backend\PDO($pdo);
 $principalBackend = new DokuWikiSabrePrincipalBackend();
 
 // Directory structure
 $tree = [
     new Sabre\CalDAV\Principal\Collection($principalBackend),
     new Sabre\CalDAV\CalendarRoot($principalBackend, $calendarBackend),
 ];
 
 $server = new Sabre\DAV\Server($tree);
 
 if (isset($baseUri))
     $server->setBaseUri($baseUri);
 
 /* Server Plugins */
 $authPlugin = new Sabre\DAV\Auth\Plugin($authBackend);
 $server->addPlugin($authPlugin);
 
 $aclPlugin = new Sabre\DAVACL\Plugin();
 $server->addPlugin($aclPlugin);
 
 /* CalDAV support */
 $caldavPlugin = new Sabre\CalDAV\Plugin();
 $server->addPlugin($caldavPlugin);
 
 /* Calendar subscription support */
-$server->addPlugin(
-    new Sabre\CalDAV\Subscriptions\Plugin()
-);
+//$server->addPlugin(
+//    new Sabre\CalDAV\Subscriptions\Plugin()
+//);
 
 /* Calendar scheduling support */
-$server->addPlugin(
-    new Sabre\CalDAV\Schedule\Plugin()
-);
+//$server->addPlugin(
+//    new Sabre\CalDAV\Schedule\Plugin()
+//);
 
 /* WebDAV-Sync plugin */
-// This breaks the way we manage our calendars - sorry
-// $server->addPlugin(new Sabre\DAV\Sync\Plugin());
+$server->addPlugin(new Sabre\DAV\Sync\Plugin());
 
 // Support for html frontend
 $browser = new Sabre\DAV\Browser\Plugin();
 $server->addPlugin($browser);
 
 // And off we go!
 $server->exec();
diff --git a/helper.php b/helper.php
--- a/helper.php
+++ b/helper.php
@@ -1,233 +1,305 @@
 <?php
 /** 
   * Helper Class for the tagrevisions plugin
   * This helper does the actual work.
   * 
   * Configurable in DokuWiki's configuration
   */
   
 // must be run within Dokuwiki
 if(!defined('DOKU_INC')) die();
 
 class helper_plugin_davcal extends DokuWiki_Plugin {
   
   protected $sqlite = null;
   
   /**
     * Constructor to load the configuration
     */
   public function helper_plugin_davcal() {
     $this->sqlite =& plugin_load('helper', 'sqlite');
     if(!$this->sqlite)
     {
         msg('This plugin requires the sqlite plugin. Please install it.');
         return;
     }
     
     if(!$this->sqlite->init('davcal', DOKU_PLUGIN.'davcal/db/'))
     {
         return;
     }
   }
   
   public function setCalendarNameForPage($name, $description, $id = null, $userid = null)
   {
       if(is_null($id))
       {
           global $ID;
           $id = $ID;
       }
       if(is_null($userid))
         $userid = $_SERVER['REMOTE_USER'];
       $calid = $this->getCalendarIdForPage($id);
       if($calid === false)
         return $this->createCalendarForPage($name, $description, $id, $userid);
       
       // Update the calendar name here
       
   }
   
   public function getCalendarIdForPage($id = null)
   {
       if(is_null($id))
       {
           global $ID;
           $id = $ID;
       }
       
       $query = "SELECT calid FROM pagetocalendarmapping WHERE page=".$this->sqlite->quote_string($id);
       $res = $this->sqlite->query($query);
       $row = $this->sqlite->res2row($res);
       if(isset($row['calid']))
         return $row['calid'];
       else
         return false;
   }
   
   public function getCalendarIdToPageMapping()
   {
       $query = "SELECT calid, page FROM pagetocalendarmapping";
       $res = $this->sqlite->query($query);
       $arr = $this->sqlite->res2arr($res);
       return $arr;
   }
   
   public function getCalendarIdsForUser($principalUri)
   {
       $user = explode('/', $principalUri);
       $user = end($user);
       $mapping = $this->getCalendarIdToPageMapping();
       $calids = array();
       foreach($mapping as $row)
       {
           $id = $row['calid'];
           $page = $row['page'];
           $acl = auth_quickaclcheck($page);
           if($acl >= AUTH_READ)
           {
               $write = $acl > AUTH_READ;
               $calids[$id] = array('readonly' => !$write);
           }
       }
       return $calids;
   }
   
   public function createCalendarForPage($name, $description, $id = null, $userid = null)
   {
       if(is_null($id))
       {
           global $ID;
           $id = $ID;
       }
       if(is_null($userid))
           $userid = $_SERVER['REMOTE_USER'];
       $values = array('principals/'.$userid, 
                       $name,
                       str_replace(array('/', ' ', ':'), '_', $id), 
                       $description,
                       'VEVENT,VTODO',
-                      0);
-      $query = "INSERT INTO calendars (principaluri, displayname, uri, description, components, transparent) VALUES (".$this->sqlite->quote_and_join($values, ',').");";
+                      0,
+                      1);
+      $query = "INSERT INTO calendars (principaluri, displayname, uri, description, components, transparent, synctoken) VALUES (".$this->sqlite->quote_and_join($values, ',').");";
       $res = $this->sqlite->query($query);
+      if($res === false)
+        return false;
       $query = "SELECT id FROM calendars WHERE principaluri=".$this->sqlite->quote_string($values[0])." AND ".
                "displayname=".$this->sqlite->quote_string($values[1])." AND ".
                "uri=".$this->sqlite->quote_string($values[2])." AND ".
                "description=".$this->sqlite->quote_string($values[3]);
       $res = $this->sqlite->query($query);
       $row = $this->sqlite->res2row($res);
       if(isset($row['id']))
       {
           $values = array($id, $row['id']);
           $query = "INSERT INTO pagetocalendarmapping (page, calid) VALUES (".$this->sqlite->quote_and_join($values, ',').")";
           $res = $this->sqlite->query($query);
-          return true;
+          return ($res !== false);
       }
       
       return false;
   }
 
   public function addCalendarEntryToCalendarForPage($id, $user, $params)
   {
       require_once('vendor/autoload.php');
       $vcalendar = new \Sabre\VObject\Component\VCalendar();
       $event = $vcalendar->add('VEVENT');
       $event->summary = $params['eventname'];
       $dtStart = new \DateTime($params['eventfrom'], new \DateTimeZone('Europe/Vienna')); // FIXME: Timezone
       $dtEnd = new \DateTime($params['eventto'], new \DateTimeZone('Europe/Vienna')); // FIXME: Timezone
       $event->DTSTART = $dtStart;
       $event->DTEND = $dtEnd;
       $calid = $this->getCalendarIdForPage($id);
       $uri = uniqid('dokuwiki-').'.ics';
       $now = new DateTime();
       $eventStr = $vcalendar->serialize();
       
       $values = array($calid,
                       $uri,
                       $eventStr,
                       $now->getTimestamp(),
                       'VEVENT',
                       $event->DTSTART->getDateTime()->getTimeStamp(),
                       $event->DTEND->getDateTime()->getTimeStamp(),
                       strlen($eventStr),
                       md5($eventStr),
                       uniqid()
       );
       
       $query = "INSERT INTO calendarobjects (calendarid, uri, calendardata, lastmodified, componenttype, firstoccurence, lastoccurence, size, etag, uid) VALUES (".$this->sqlite->quote_and_join($values, ',').")";
       $res = $this->sqlite->query($query);
-      return true;
+      if($res !== false)
+      {
+          $this->updateSyncTokenLog($calid, $uri, 'added');
+          return true;
+      }
+      return false;
   }
 
   public function getEventsWithinDateRange($id, $user, $startDate, $endDate)
   {
       $data = array();
       require_once('vendor/autoload.php');
       $calid = $this->getCalendarIdForPage($id);
       $startTs = new \DateTime($startDate);
       $endTs = new \DateTime($endDate);
       $query = "SELECT calendardata, componenttype, uid FROM calendarobjects WHERE calendarid=".
                 $this->sqlite->quote_string($calid)." AND firstoccurence > ".
                 $this->sqlite->quote_string($startTs->getTimestamp())." AND firstoccurence < ".
                 $this->sqlite->quote_string($endTs->getTimestamp());
       $res = $this->sqlite->query($query);
       $arr = $this->sqlite->res2arr($res);
       foreach($arr as $row)
       {
           if(isset($row['calendardata']))
           {
               $vcal = \Sabre\VObject\Reader::read($row['calendardata']);
               $start = $vcal->VEVENT->DTSTART->getDateTime();
               $end = $vcal->VEVENT->DTEND->getDateTime();
               $summary = (string)$vcal->VEVENT->summary;
               $data[] = array("title" => $summary, "start" => $start->format(\DateTime::W3C),
                               "end" => $end->format(\DateTime::W3C),
                               "id" => $row['uid']);
           }
       }
       return $data;
   }
   
   public function getEventWithUid($uid)
   {
-      $query = "SELECT calendardata, componenttype FROM calendarobjects WHERE uid=".
+      $query = "SELECT calendardata, calendarid, componenttype, uri FROM calendarobjects WHERE uid=".
                 $this->sqlite->quote_string($uid);
       $res = $this->sqlite->query($query);
       $row = $this->sqlite->res2row($res);
       return $row;
   }
   
   public function editCalendarEntryForPage($id, $user, $params)
   {
-      $event = $this->getEventWithUid($params['uid']);
+      $uid = $params['uid'];
+      $event = $this->getEventWithUid($uid);
       require_once('vendor/autoload.php');
       if(!isset($event['calendardata']))
         return false;
+      $uri = $event['uri'];
+      $calid = $event['calendarid'];
       $vcal = \Sabre\VObject\Reader::read($event['calendardata']);
       $vcal->VEVENT->summary = $params['eventname'];
       $dtStart = new \DateTime($params['eventfrom'], new \DateTimeZone('Europe/Vienna')); // FIXME: Timezone
       $dtEnd = new \DateTime($params['eventto'], new \DateTimeZone('Europe/Vienna')); // FIXME: Timezone
       $vcal->VEVENT->DTSTART = $dtStart;
       $vcal->VEVENT->DTEND = $dtEnd;
       $now = new DateTime();
       $eventStr = $vcal->serialize();
       
       $query = "UPDATE calendarobjects SET calendardata=".$this->sqlite->quote_string($eventStr).
                ", lastmodified=".$this->sqlite->quote_string($now->getTimestamp()).
                ", firstoccurence=".$this->sqlite->quote_string($dtStart->getTimestamp()).
                ", lastoccurence=".$this->sqlite->quote_string($dtEnd->getTimestamp()).
                ", size=".strlen($eventStr).
                ", etag=".$this->sqlite->quote_string(md5($eventStr)).
-               " WHERE uid=".$this->sqlite->quote_string($params['uid']);
+               " WHERE uid=".$this->sqlite->quote_string($uid);
       $res = $this->sqlite->query($query);
-      return true;
+      if($res !== false)
+      {
+          $this->updateSyncTokenLog($calid, $uri, 'modified');
+          return true;
+      }
+      return false;
   }
 
   public function deleteCalendarEntryForPage($id, $params)
   {
       $uid = $params['uid'];
+      $event = $this->getEventWithUid($uid);
+      $uri = $event['uri'];
       $query = "DELETE FROM calendarobjects WHERE uid=".$this->sqlite->quote_string($uid);
       $res = $this->sqlite->query($query);
+      if($res !== false)
+      {
+          $this->updateSyncTokenLog($calid, $uri, 'deleted');
+      }
       return true;
   }
   
+  public function getSyncTokenForCalendar($calid)
+  {
+      $query = "SELECT synctoken FROM calendars WHERE id=".$this->sqlite->quote_string($calid);
+      $res = $this->sqlite->query($query);
+      $row = $this->sqlite->res2row($res);
+      if(isset($row['synctoken']))
+          return $row['synctoken'];
+      return false;
+  }
+  
+  public function operationNameToOperation($operationName)
+  {
+      switch($operationName)
+      {
+          case 'added':
+              return 1;
+          break;
+          case 'modified':
+              return 2;
+          break;
+          case 'deleted':
+              return 3;
+          break;
+      }
+      return false;
+  }
+  
+  private function updateSyncTokenLog($calid, $uri, $operation)
+  {
+      $currentToken = $this->getSyncTokenForCalendar($calid);
+      $operationCode = $this->operationNameToOperation($operation);
+      if(($operationCode === false) || ($currentToken === false))
+          return false;
+      $values = array($uri,
+                      $currentToken,
+                      $calid,
+                      $operationCode
+      );
+      $query = "INSERT INTO calendarchanges (uri, synctoken, calendarid, operation) VALUES(".
+               $this->sqlite->quote_and_join($values, ',').")";
+      $res = $this->sqlite->query($query);
+      if($res === false)
+        return false;
+      $currentToken++;
+      $query = "UPDATE calendars SET synctoken=".$this->sqlite->quote_string($currentToken)." WHERE id=".
+               $this->sqlite->quote_string($calid);
+      $res = $this->sqlite->query($query);
+      return ($res !== false);
+  }
+  
 }