diff --git a/Event.php b/Event.php
index b97b986..9e1b896 100644
--- a/Event.php
+++ b/Event.php
@@ -79,6 +79,10 @@ class Event
      */
     protected $_callable      = [];
 
+    /**
+     * @var array
+     */
+    protected $_priorities = [];
 
 
     /**
@@ -186,10 +190,23 @@ public static function unregister($eventId, $hard = false)
      * @param   mixed   $callable    Callable.
      * @return  \Hoa\Event\Event
      */
-    public function attach($callable)
+    public function attach($callable, $priority = 0)
     {
-        $callable                              = xcallable($callable);
-        $this->_callable[$callable->getHash()] = $callable;
+        $callable                 = xcallable($callable);
+        $hash                     = $callable->getHash();
+        $this->_callable[$hash]   = $callable;
+        $this->_priorities[$hash] = (int) $priority;
+
+        uksort($this->_callable, function ($a, $b) {
+            $a = $this->_priorities[$a];
+            $b = $this->_priorities[$b];
+
+            /*if (70000 <= PHP_VERSION_ID) {
+                return $this->_priorities[$ka] <=> $this->_priorities[$kb];
+            }*/
+
+            return  ($a < $b) ? 1 : (($a > $b) ? -1 : 0);
+        });
 
         return $this;
     }
diff --git a/Test/Unit/Event.php b/Test/Unit/Event.php
index 769d22a..210aa6d 100644
--- a/Test/Unit/Event.php
+++ b/Test/Unit/Event.php
@@ -186,6 +186,47 @@ public function case_attach()
                     ->isIdenticalTo($event)
                 ->boolean($event->isListened())
                     ->isTrue();
+
+        $this
+            ->given(
+                $eventId = 'hoa://Event/Test',
+                $source  = new \Mock\Hoa\Event\Source(),
+                $bucket  = new LUT\Bucket(),
+                $called  = '',
+
+                SUT::register($eventId, $source),
+                SUT::getEvent($eventId)->attach(
+                    function (LUT\Bucket $receivedBucket) use (&$called) {
+                        $called .= '1';
+                    }, 100
+                ),
+                SUT::getEvent($eventId)->attach(
+                    function (LUT\Bucket $receivedBucket) use (&$called) {
+                        $called .= '2';
+                    }, 10
+                ),
+                SUT::getEvent($eventId)->attach(
+                    function (LUT\Bucket $receivedBucket) use (&$called) {
+                        $called .= '3';
+                    }
+                ),
+                SUT::getEvent($eventId)->attach(
+                    function (LUT\Bucket $receivedBucket) use (&$called) {
+                        $called .= '3';
+                    }, 0
+                ),
+                SUT::getEvent($eventId)->attach(
+                    function (LUT\Bucket $receivedBucket) use (&$called) {
+                        $called .= '4';
+                    }, -1
+                )
+            )
+            ->when($result = SUT::notify($eventId, $source, $bucket))
+            ->then
+                ->variable($result)
+                    ->isNull()
+                ->string($called)
+                    ->isIdenticalTo('12334');
     }
 
     public function case_detach()