diff --git a/src/applications/calendar/controller/PhabricatorCalendarEventJoinController.php b/src/applications/calendar/controller/PhabricatorCalendarEventJoinController.php
--- a/src/applications/calendar/controller/PhabricatorCalendarEventJoinController.php
+++ b/src/applications/calendar/controller/PhabricatorCalendarEventJoinController.php
@@ -3,18 +3,9 @@
 final class PhabricatorCalendarEventJoinController
   extends PhabricatorCalendarController {
 
-  const ACTION_ACCEPT = 'accept';
-  const ACTION_DECLINE = 'decline';
-  const ACTION_JOIN = 'join';
-
   public function handleRequest(AphrontRequest $request) {
+    $viewer = $this->getViewer();
     $id = $request->getURIData('id');
-    $action = $request->getURIData('action');
-
-    $request = $this->getRequest();
-    $viewer = $request->getViewer();
-    $declined_status = PhabricatorCalendarEventInvitee::STATUS_DECLINED;
-    $attending_status = PhabricatorCalendarEventInvitee::STATUS_ATTENDING;
 
     $event = id(new PhabricatorCalendarEventQuery())
       ->setViewer($viewer)
@@ -25,34 +16,31 @@
     }
 
     $cancel_uri = $event->getURI();
-    $validation_exception = null;
 
-    $is_attending = $event->getIsUserAttending($viewer->getPHID());
+    $action = $request->getURIData('action');
+    switch ($action) {
+      case 'accept':
+        $is_join = true;
+        break;
+      case 'decline':
+        $is_join = false;
+        break;
+      default:
+        $is_join = !$event->getIsUserAttending($viewer->getPHID());
+        break;
+    }
 
+    $validation_exception = null;
     if ($request->isFormPost()) {
-      $new_status = null;
-
-      switch ($action) {
-        case self::ACTION_ACCEPT:
-          $new_status = $attending_status;
-          break;
-        case self::ACTION_JOIN:
-          if ($is_attending) {
-            $new_status = $declined_status;
-          } else {
-            $new_status = $attending_status;
-          }
-          break;
-        case self::ACTION_DECLINE:
-          $new_status = $declined_status;
-          break;
+      if ($is_join) {
+        $xaction_type = PhabricatorCalendarEventTransaction::TYPE_ACCEPT;
+      } else {
+        $xaction_type = PhabricatorCalendarEventTransaction::TYPE_DECLINE;
       }
 
-      $new_status = array($viewer->getPHID() => $new_status);
-
       $xaction = id(new PhabricatorCalendarEventTransaction())
-        ->setTransactionType(PhabricatorCalendarEventTransaction::TYPE_INVITE)
-        ->setNewValue($new_status);
+        ->setTransactionType($xaction_type)
+        ->setNewValue(true);
 
       $editor = id(new PhabricatorCalendarEventEditor())
         ->setActor($viewer)
@@ -68,8 +56,7 @@
       }
     }
 
-    if (($action == self::ACTION_JOIN && !$is_attending)
-      || $action == self::ACTION_ACCEPT) {
+    if ($is_join) {
       $title = pht('Join Event');
       $paragraph = pht('Would you like to join this event?');
       $submit = pht('Join');
diff --git a/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php b/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php
--- a/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php
+++ b/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php
@@ -68,6 +68,8 @@
     $types[] = PhabricatorCalendarEventTransaction::TYPE_INVITE;
     $types[] = PhabricatorCalendarEventTransaction::TYPE_ALL_DAY;
     $types[] = PhabricatorCalendarEventTransaction::TYPE_ICON;
+    $types[] = PhabricatorCalendarEventTransaction::TYPE_ACCEPT;
+    $types[] = PhabricatorCalendarEventTransaction::TYPE_DECLINE;
 
     $types[] = PhabricatorCalendarEventTransaction::TYPE_RECURRING;
     $types[] = PhabricatorCalendarEventTransaction::TYPE_FREQUENCY;
@@ -104,6 +106,10 @@
         return (int)$object->getIsAllDay();
       case PhabricatorCalendarEventTransaction::TYPE_ICON:
         return $object->getIcon();
+      case PhabricatorCalendarEventTransaction::TYPE_ACCEPT:
+      case PhabricatorCalendarEventTransaction::TYPE_DECLINE:
+        $actor_phid = $this->getActingAsPHID();
+        return $object->getUserInviteStatus($actor_phid);
       case PhabricatorCalendarEventTransaction::TYPE_INVITE:
         $map = $xaction->getNewValue();
         $phids = array_keys($map);
@@ -136,6 +142,10 @@
       case PhabricatorCalendarEventTransaction::TYPE_INVITE:
       case PhabricatorCalendarEventTransaction::TYPE_ICON:
         return $xaction->getNewValue();
+      case PhabricatorCalendarEventTransaction::TYPE_ACCEPT:
+        return PhabricatorCalendarEventInvitee::STATUS_ATTENDING;
+      case PhabricatorCalendarEventTransaction::TYPE_DECLINE:
+        return PhabricatorCalendarEventInvitee::STATUS_DECLINED;
       case PhabricatorCalendarEventTransaction::TYPE_ALL_DAY:
         return (int)$xaction->getNewValue();
       case PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE:
@@ -181,6 +191,8 @@
         $object->setIcon($xaction->getNewValue());
         return;
       case PhabricatorCalendarEventTransaction::TYPE_INVITE:
+      case PhabricatorCalendarEventTransaction::TYPE_ACCEPT:
+      case PhabricatorCalendarEventTransaction::TYPE_DECLINE:
         return;
     }
 
@@ -223,6 +235,28 @@
         }
         $object->attachInvitees($invitees);
         return;
+      case PhabricatorCalendarEventTransaction::TYPE_ACCEPT:
+      case PhabricatorCalendarEventTransaction::TYPE_DECLINE:
+        $acting_phid = $this->getActingAsPHID();
+
+        $invitees = $object->getInvitees();
+        $invitees = mpull($invitees, null, 'getInviteePHID');
+
+        $invitee = idx($invitees, $acting_phid);
+        if (!$invitee) {
+          $invitee = id(new PhabricatorCalendarEventInvitee())
+            ->setEventPHID($object->getPHID())
+            ->setInviteePHID($acting_phid)
+            ->setInviterPHID($acting_phid);
+          $invitees[$acting_phid] = $invitee;
+        }
+
+        $invitee
+          ->setStatus($xaction->getNewValue())
+          ->save();
+
+        $object->attachInvitees($invitees);
+        return;
     }
 
     return parent::applyCustomExternalTransaction($object, $xaction);
@@ -252,6 +286,12 @@
           // caches for all attendees.
           $invalidate_all = true;
           break;
+
+        case PhabricatorCalendarEventTransaction::TYPE_ACCEPT:
+        case PhabricatorCalendarEventTransaction::TYPE_DECLINE:
+          $acting_phid = $this->getActingAsPHID();
+          $invalidate_phids[$acting_phid] = $acting_phid;
+          break;
         case PhabricatorCalendarEventTransaction::TYPE_INVITE:
           foreach ($xaction->getNewValue() as $phid => $ignored) {
             $invalidate_phids[$phid] = $phid;
diff --git a/src/applications/calendar/storage/PhabricatorCalendarEventTransaction.php b/src/applications/calendar/storage/PhabricatorCalendarEventTransaction.php
--- a/src/applications/calendar/storage/PhabricatorCalendarEventTransaction.php
+++ b/src/applications/calendar/storage/PhabricatorCalendarEventTransaction.php
@@ -11,11 +11,14 @@
   const TYPE_ALL_DAY = 'calendar.allday';
   const TYPE_ICON = 'calendar.icon';
   const TYPE_INVITE = 'calendar.invite';
+  const TYPE_ACCEPT = 'calendar.accept';
+  const TYPE_DECLINE = 'calendar.decline';
 
   const TYPE_RECURRING = 'calendar.recurring';
   const TYPE_FREQUENCY = 'calendar.frequency';
   const TYPE_RECURRENCE_END_DATE = 'calendar.recurrenceenddate';
 
+
   const MAILTAG_RESCHEDULE = 'calendar-reschedule';
   const MAILTAG_CONTENT = 'calendar-content';
   const MAILTAG_OTHER = 'calendar-other';
@@ -163,6 +166,14 @@
             '%s reinstated this event.',
             $this->renderHandleLink($author_phid));
         }
+      case self::TYPE_ACCEPT:
+        return pht(
+          '%s is attending this event.',
+          $this->renderHandleLink($author_phid));
+      case self::TYPE_DECLINE:
+        return pht(
+          '%s declined this event.',
+          $this->renderHandleLink($author_phid));
       case self::TYPE_INVITE:
         $text = null;
 
@@ -363,6 +374,16 @@
             $this->renderHandleLink($author_phid),
             $this->renderHandleLink($object_phid));
         }
+      case self::TYPE_ACCEPT:
+        return pht(
+          '%s is attending %s.',
+          $this->renderHandleLink($author_phid),
+          $this->renderHandleLink($object_phid));
+      case self::TYPE_DECLINE:
+        return pht(
+          '%s declined %s.',
+          $this->renderHandleLink($author_phid),
+          $this->renderHandleLink($object_phid));
       case self::TYPE_INVITE:
         $text = null;