diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -2021,24 +2021,40 @@
     'PhabricatorCalendarDAO' => 'applications/calendar/storage/PhabricatorCalendarDAO.php',
     'PhabricatorCalendarEditEngine' => 'applications/calendar/editor/PhabricatorCalendarEditEngine.php',
     'PhabricatorCalendarEvent' => 'applications/calendar/storage/PhabricatorCalendarEvent.php',
+    'PhabricatorCalendarEventAcceptTransaction' => 'applications/calendar/xaction/PhabricatorCalendarEventAcceptTransaction.php',
+    'PhabricatorCalendarEventAllDayTransaction' => 'applications/calendar/xaction/PhabricatorCalendarEventAllDayTransaction.php',
     'PhabricatorCalendarEventCancelController' => 'applications/calendar/controller/PhabricatorCalendarEventCancelController.php',
+    'PhabricatorCalendarEventCancelTransaction' => 'applications/calendar/xaction/PhabricatorCalendarEventCancelTransaction.php',
+    'PhabricatorCalendarEventDateTransaction' => 'applications/calendar/xaction/PhabricatorCalendarEventDateTransaction.php',
+    'PhabricatorCalendarEventDeclineTransaction' => 'applications/calendar/xaction/PhabricatorCalendarEventDeclineTransaction.php',
+    'PhabricatorCalendarEventDescriptionTransaction' => 'applications/calendar/xaction/PhabricatorCalendarEventDescriptionTransaction.php',
     'PhabricatorCalendarEventDragController' => 'applications/calendar/controller/PhabricatorCalendarEventDragController.php',
     'PhabricatorCalendarEventEditController' => 'applications/calendar/controller/PhabricatorCalendarEventEditController.php',
     'PhabricatorCalendarEventEditor' => 'applications/calendar/editor/PhabricatorCalendarEventEditor.php',
     'PhabricatorCalendarEventEmailCommand' => 'applications/calendar/command/PhabricatorCalendarEventEmailCommand.php',
+    'PhabricatorCalendarEventEndDateTransaction' => 'applications/calendar/xaction/PhabricatorCalendarEventEndDateTransaction.php',
+    'PhabricatorCalendarEventFrequencyTransaction' => 'applications/calendar/xaction/PhabricatorCalendarEventFrequencyTransaction.php',
     'PhabricatorCalendarEventFulltextEngine' => 'applications/calendar/search/PhabricatorCalendarEventFulltextEngine.php',
+    'PhabricatorCalendarEventIconTransaction' => 'applications/calendar/xaction/PhabricatorCalendarEventIconTransaction.php',
+    'PhabricatorCalendarEventInviteTransaction' => 'applications/calendar/xaction/PhabricatorCalendarEventInviteTransaction.php',
     'PhabricatorCalendarEventInvitee' => 'applications/calendar/storage/PhabricatorCalendarEventInvitee.php',
     'PhabricatorCalendarEventInviteeQuery' => 'applications/calendar/query/PhabricatorCalendarEventInviteeQuery.php',
     'PhabricatorCalendarEventJoinController' => 'applications/calendar/controller/PhabricatorCalendarEventJoinController.php',
     'PhabricatorCalendarEventListController' => 'applications/calendar/controller/PhabricatorCalendarEventListController.php',
     'PhabricatorCalendarEventMailReceiver' => 'applications/calendar/mail/PhabricatorCalendarEventMailReceiver.php',
+    'PhabricatorCalendarEventNameTransaction' => 'applications/calendar/xaction/PhabricatorCalendarEventNameTransaction.php',
     'PhabricatorCalendarEventPHIDType' => 'applications/calendar/phid/PhabricatorCalendarEventPHIDType.php',
     'PhabricatorCalendarEventQuery' => 'applications/calendar/query/PhabricatorCalendarEventQuery.php',
     'PhabricatorCalendarEventRSVPEmailCommand' => 'applications/calendar/command/PhabricatorCalendarEventRSVPEmailCommand.php',
+    'PhabricatorCalendarEventRecurringTransaction' => 'applications/calendar/xaction/PhabricatorCalendarEventRecurringTransaction.php',
+    'PhabricatorCalendarEventReplyTransaction' => 'applications/calendar/xaction/PhabricatorCalendarEventReplyTransaction.php',
     'PhabricatorCalendarEventSearchEngine' => 'applications/calendar/query/PhabricatorCalendarEventSearchEngine.php',
+    'PhabricatorCalendarEventStartDateTransaction' => 'applications/calendar/xaction/PhabricatorCalendarEventStartDateTransaction.php',
     'PhabricatorCalendarEventTransaction' => 'applications/calendar/storage/PhabricatorCalendarEventTransaction.php',
     'PhabricatorCalendarEventTransactionComment' => 'applications/calendar/storage/PhabricatorCalendarEventTransactionComment.php',
     'PhabricatorCalendarEventTransactionQuery' => 'applications/calendar/query/PhabricatorCalendarEventTransactionQuery.php',
+    'PhabricatorCalendarEventTransactionType' => 'applications/calendar/xaction/PhabricatorCalendarEventTransactionType.php',
+    'PhabricatorCalendarEventUntilDateTransaction' => 'applications/calendar/xaction/PhabricatorCalendarEventUntilDateTransaction.php',
     'PhabricatorCalendarEventViewController' => 'applications/calendar/controller/PhabricatorCalendarEventViewController.php',
     'PhabricatorCalendarHoliday' => 'applications/calendar/storage/PhabricatorCalendarHoliday.php',
     'PhabricatorCalendarHolidayTestCase' => 'applications/calendar/storage/__tests__/PhabricatorCalendarHolidayTestCase.php',
@@ -6629,12 +6645,22 @@
       'PhabricatorSpacesInterface',
       'PhabricatorFulltextInterface',
     ),
+    'PhabricatorCalendarEventAcceptTransaction' => 'PhabricatorCalendarEventReplyTransaction',
+    'PhabricatorCalendarEventAllDayTransaction' => 'PhabricatorCalendarEventTransactionType',
     'PhabricatorCalendarEventCancelController' => 'PhabricatorCalendarController',
+    'PhabricatorCalendarEventCancelTransaction' => 'PhabricatorCalendarEventTransactionType',
+    'PhabricatorCalendarEventDateTransaction' => 'PhabricatorCalendarEventTransactionType',
+    'PhabricatorCalendarEventDeclineTransaction' => 'PhabricatorCalendarEventReplyTransaction',
+    'PhabricatorCalendarEventDescriptionTransaction' => 'PhabricatorCalendarEventTransactionType',
     'PhabricatorCalendarEventDragController' => 'PhabricatorCalendarController',
     'PhabricatorCalendarEventEditController' => 'PhabricatorCalendarController',
     'PhabricatorCalendarEventEditor' => 'PhabricatorApplicationTransactionEditor',
     'PhabricatorCalendarEventEmailCommand' => 'MetaMTAEmailTransactionCommand',
+    'PhabricatorCalendarEventEndDateTransaction' => 'PhabricatorCalendarEventDateTransaction',
+    'PhabricatorCalendarEventFrequencyTransaction' => 'PhabricatorCalendarEventTransactionType',
     'PhabricatorCalendarEventFulltextEngine' => 'PhabricatorFulltextEngine',
+    'PhabricatorCalendarEventIconTransaction' => 'PhabricatorCalendarEventTransactionType',
+    'PhabricatorCalendarEventInviteTransaction' => 'PhabricatorCalendarEventTransactionType',
     'PhabricatorCalendarEventInvitee' => array(
       'PhabricatorCalendarDAO',
       'PhabricatorPolicyInterface',
@@ -6643,13 +6669,19 @@
     'PhabricatorCalendarEventJoinController' => 'PhabricatorCalendarController',
     'PhabricatorCalendarEventListController' => 'PhabricatorCalendarController',
     'PhabricatorCalendarEventMailReceiver' => 'PhabricatorObjectMailReceiver',
+    'PhabricatorCalendarEventNameTransaction' => 'PhabricatorCalendarEventTransactionType',
     'PhabricatorCalendarEventPHIDType' => 'PhabricatorPHIDType',
     'PhabricatorCalendarEventQuery' => 'PhabricatorCursorPagedPolicyAwareQuery',
     'PhabricatorCalendarEventRSVPEmailCommand' => 'PhabricatorCalendarEventEmailCommand',
+    'PhabricatorCalendarEventRecurringTransaction' => 'PhabricatorCalendarEventTransactionType',
+    'PhabricatorCalendarEventReplyTransaction' => 'PhabricatorCalendarEventTransactionType',
     'PhabricatorCalendarEventSearchEngine' => 'PhabricatorApplicationSearchEngine',
-    'PhabricatorCalendarEventTransaction' => 'PhabricatorApplicationTransaction',
+    'PhabricatorCalendarEventStartDateTransaction' => 'PhabricatorCalendarEventDateTransaction',
+    'PhabricatorCalendarEventTransaction' => 'PhabricatorModularTransaction',
     'PhabricatorCalendarEventTransactionComment' => 'PhabricatorApplicationTransactionComment',
     'PhabricatorCalendarEventTransactionQuery' => 'PhabricatorApplicationTransactionQuery',
+    'PhabricatorCalendarEventTransactionType' => 'PhabricatorModularTransactionType',
+    'PhabricatorCalendarEventUntilDateTransaction' => 'PhabricatorCalendarEventDateTransaction',
     'PhabricatorCalendarEventViewController' => 'PhabricatorCalendarController',
     'PhabricatorCalendarHoliday' => 'PhabricatorCalendarDAO',
     'PhabricatorCalendarHolidayTestCase' => 'PhabricatorTestCase',
diff --git a/src/applications/calendar/command/PhabricatorCalendarEventRSVPEmailCommand.php b/src/applications/calendar/command/PhabricatorCalendarEventRSVPEmailCommand.php
--- a/src/applications/calendar/command/PhabricatorCalendarEventRSVPEmailCommand.php
+++ b/src/applications/calendar/command/PhabricatorCalendarEventRSVPEmailCommand.php
@@ -44,32 +44,24 @@
     PhabricatorMetaMTAReceivedMail $mail,
     $command,
     array $argv) {
-    $status_attending = PhabricatorCalendarEventInvitee::STATUS_ATTENDING;
-    $status_declined = PhabricatorCalendarEventInvitee::STATUS_DECLINED;
-    $xactions = array();
 
     $target = phutil_utf8_strtolower(implode(' ', $argv));
-    $rsvp = null;
 
     $yes_values = $this->getYesValues();
     $no_values = $this->getNoValues();
 
     if (in_array($target, $yes_values)) {
-      $rsvp = $status_attending;
+      $rsvp = PhabricatorCalendarEventAcceptTransaction::TRANSACTIONTYPE;
     } else if (in_array($target, $no_values)) {
-      $rsvp = $status_declined;
+      $rsvp = PhabricatorCalendarEventDeclineTransaction::TRANSACTIONTYPE;
     } else {
-      $rsvp = null;
-    }
-
-    if ($rsvp === null) {
       return array();
     }
 
+    $xactions = array();
     $xactions[] = $object->getApplicationTransactionTemplate()
-      ->setTransactionType(PhabricatorCalendarEventTransaction::TYPE_INVITE)
-      ->setNewValue(array($viewer->getPHID() => $rsvp));
-
+      ->setTransactionType($rsvp)
+      ->setNewValue(true);
     return $xactions;
   }
 
diff --git a/src/applications/calendar/controller/PhabricatorCalendarEventCancelController.php b/src/applications/calendar/controller/PhabricatorCalendarEventCancelController.php
--- a/src/applications/calendar/controller/PhabricatorCalendarEventCancelController.php
+++ b/src/applications/calendar/controller/PhabricatorCalendarEventCancelController.php
@@ -38,7 +38,7 @@
 
       $xaction = id(new PhabricatorCalendarEventTransaction())
         ->setTransactionType(
-          PhabricatorCalendarEventTransaction::TYPE_CANCEL)
+          PhabricatorCalendarEventCancelTransaction::TRANSACTIONTYPE)
         ->setNewValue(!$is_cancelled);
 
       $editor = id(new PhabricatorCalendarEventEditor())
diff --git a/src/applications/calendar/controller/PhabricatorCalendarEventDragController.php b/src/applications/calendar/controller/PhabricatorCalendarEventDragController.php
--- a/src/applications/calendar/controller/PhabricatorCalendarEventDragController.php
+++ b/src/applications/calendar/controller/PhabricatorCalendarEventDragController.php
@@ -41,13 +41,14 @@
       $viewer,
       $end));
 
-
     $xactions[] = id(new PhabricatorCalendarEventTransaction())
-      ->setTransactionType(PhabricatorCalendarEventTransaction::TYPE_START_DATE)
+      ->setTransactionType(
+        PhabricatorCalendarEventStartDateTransaction::TRANSACTIONTYPE)
       ->setNewValue($start_value);
 
     $xactions[] = id(new PhabricatorCalendarEventTransaction())
-      ->setTransactionType(PhabricatorCalendarEventTransaction::TYPE_END_DATE)
+      ->setTransactionType(
+        PhabricatorCalendarEventEndDateTransaction::TRANSACTIONTYPE)
       ->setNewValue($end_value);
 
     $editor = id(new PhabricatorCalendarEventEditor())
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
@@ -33,9 +33,11 @@
     $validation_exception = null;
     if ($request->isFormPost()) {
       if ($is_join) {
-        $xaction_type = PhabricatorCalendarEventTransaction::TYPE_ACCEPT;
+        $xaction_type =
+          PhabricatorCalendarEventAcceptTransaction::TRANSACTIONTYPE;
       } else {
-        $xaction_type = PhabricatorCalendarEventTransaction::TYPE_DECLINE;
+        $xaction_type =
+          PhabricatorCalendarEventDeclineTransaction::TRANSACTIONTYPE;
       }
 
       $xaction = id(new PhabricatorCalendarEventTransaction())
diff --git a/src/applications/calendar/controller/PhabricatorCalendarEventViewController.php b/src/applications/calendar/controller/PhabricatorCalendarEventViewController.php
--- a/src/applications/calendar/controller/PhabricatorCalendarEventViewController.php
+++ b/src/applications/calendar/controller/PhabricatorCalendarEventViewController.php
@@ -120,7 +120,7 @@
     if ($event->isChildEvent()) {
       $edit_label = pht('Edit This Instance');
     } else {
-      $edit_label = pht('Edit');
+      $edit_label = pht('Edit Event');
     }
 
     $curtain = $this->newCurtainView($event);
diff --git a/src/applications/calendar/editor/PhabricatorCalendarEditEngine.php b/src/applications/calendar/editor/PhabricatorCalendarEditEngine.php
--- a/src/applications/calendar/editor/PhabricatorCalendarEditEngine.php
+++ b/src/applications/calendar/editor/PhabricatorCalendarEditEngine.php
@@ -81,7 +81,8 @@
         ->setLabel(pht('Name'))
         ->setDescription(pht('Name of the event.'))
         ->setIsRequired(true)
-        ->setTransactionType(PhabricatorCalendarEventTransaction::TYPE_NAME)
+        ->setTransactionType(
+          PhabricatorCalendarEventNameTransaction::TRANSACTIONTYPE)
         ->setConduitDescription(pht('Rename the event.'))
         ->setConduitTypeDescription(pht('New event name.'))
         ->setValue($object->getName()),
@@ -90,7 +91,7 @@
         ->setLabel(pht('Description'))
         ->setDescription(pht('Description of the event.'))
         ->setTransactionType(
-          PhabricatorCalendarEventTransaction::TYPE_DESCRIPTION)
+          PhabricatorCalendarEventDescriptionTransaction::TRANSACTIONTYPE)
         ->setConduitDescription(pht('Update the event description.'))
         ->setConduitTypeDescription(pht('New event description.'))
         ->setValue($object->getDescription()),
@@ -100,7 +101,7 @@
         ->setLabel(pht('Cancelled'))
         ->setDescription(pht('Cancel the event.'))
         ->setTransactionType(
-          PhabricatorCalendarEventTransaction::TYPE_CANCEL)
+          PhabricatorCalendarEventCancelTransaction::TRANSACTIONTYPE)
         ->setIsConduitOnly(true)
         ->setConduitDescription(pht('Cancel or restore the event.'))
         ->setConduitTypeDescription(pht('True to cancel the event.'))
@@ -110,7 +111,8 @@
         ->setAliases(array('invite', 'invitee', 'invitees', 'inviteePHID'))
         ->setLabel(pht('Invitees'))
         ->setDatasource(new PhabricatorMetaMTAMailableDatasource())
-        ->setTransactionType(PhabricatorCalendarEventTransaction::TYPE_INVITE)
+        ->setTransactionType(
+          PhabricatorCalendarEventInviteTransaction::TRANSACTIONTYPE)
         ->setDescription(pht('Users invited to the event.'))
         ->setConduitDescription(pht('Change invited users.'))
         ->setConduitTypeDescription(pht('New event invitees.'))
@@ -124,7 +126,7 @@
         ->setLabel(pht('Recurring'))
         ->setOptions(pht('One-Time Event'), pht('Recurring Event'))
         ->setTransactionType(
-          PhabricatorCalendarEventTransaction::TYPE_RECURRING)
+          PhabricatorCalendarEventRecurringTransaction::TRANSACTIONTYPE)
         ->setDescription(pht('One time or recurring event.'))
         ->setConduitDescription(pht('Make the event recurring.'))
         ->setConduitTypeDescription(pht('Mark the event as a recurring event.'))
@@ -135,7 +137,7 @@
         ->setLabel(pht('Frequency'))
         ->setOptions($frequency_options)
         ->setTransactionType(
-          PhabricatorCalendarEventTransaction::TYPE_FREQUENCY)
+          PhabricatorCalendarEventFrequencyTransaction::TRANSACTIONTYPE)
         ->setDescription(pht('Recurring event frequency.'))
         ->setConduitDescription(pht('Change the event frequency.'))
         ->setConduitTypeDescription(pht('New event frequency.'))
@@ -148,7 +150,7 @@
         ->setKey('until')
         ->setLabel(pht('Repeat Until'))
         ->setTransactionType(
-          PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE)
+          PhabricatorCalendarEventUntilDateTransaction::TRANSACTIONTYPE)
         ->setDescription(pht('Last instance of the event.'))
         ->setConduitDescription(pht('Change when the event repeats until.'))
         ->setConduitTypeDescription(pht('New final event time.'))
@@ -159,7 +161,8 @@
         ->setKey('isAllDay')
         ->setLabel(pht('All Day'))
         ->setOptions(pht('Normal Event'), pht('All Day Event'))
-        ->setTransactionType(PhabricatorCalendarEventTransaction::TYPE_ALL_DAY)
+        ->setTransactionType(
+          PhabricatorCalendarEventAllDayTransaction::TRANSACTIONTYPE)
         ->setDescription(pht('Marks this as an all day event.'))
         ->setConduitDescription(pht('Make the event an all day event.'))
         ->setConduitTypeDescription(pht('Mark the event as an all day event.'))
@@ -169,7 +172,7 @@
         ->setKey('start')
         ->setLabel(pht('Start'))
         ->setTransactionType(
-          PhabricatorCalendarEventTransaction::TYPE_START_DATE)
+          PhabricatorCalendarEventStartDateTransaction::TRANSACTIONTYPE)
         ->setDescription(pht('Start time of the event.'))
         ->setConduitDescription(pht('Change the start time of the event.'))
         ->setConduitTypeDescription(pht('New event start time.'))
@@ -179,7 +182,7 @@
         ->setKey('end')
         ->setLabel(pht('End'))
         ->setTransactionType(
-          PhabricatorCalendarEventTransaction::TYPE_END_DATE)
+          PhabricatorCalendarEventEndDateTransaction::TRANSACTIONTYPE)
         ->setDescription(pht('End time of the event.'))
         ->setConduitDescription(pht('Change the end time of the event.'))
         ->setConduitTypeDescription(pht('New event end time.'))
@@ -189,7 +192,8 @@
         ->setKey('icon')
         ->setLabel(pht('Icon'))
         ->setIconSet(new PhabricatorCalendarIconSet())
-        ->setTransactionType(PhabricatorCalendarEventTransaction::TYPE_ICON)
+        ->setTransactionType(
+          PhabricatorCalendarEventIconTransaction::TRANSACTIONTYPE)
         ->setDescription(pht('Event icon.'))
         ->setConduitDescription(pht('Change the event icon.'))
         ->setConduitTypeDescription(pht('New event icon.'))
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
@@ -58,21 +58,6 @@
   public function getTransactionTypes() {
     $types = parent::getTransactionTypes();
 
-    $types[] = PhabricatorCalendarEventTransaction::TYPE_NAME;
-    $types[] = PhabricatorCalendarEventTransaction::TYPE_START_DATE;
-    $types[] = PhabricatorCalendarEventTransaction::TYPE_END_DATE;
-    $types[] = PhabricatorCalendarEventTransaction::TYPE_DESCRIPTION;
-    $types[] = PhabricatorCalendarEventTransaction::TYPE_CANCEL;
-    $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;
-    $types[] = PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE;
-
     $types[] = PhabricatorTransactions::TYPE_COMMENT;
     $types[] = PhabricatorTransactions::TYPE_VIEW_POLICY;
     $types[] = PhabricatorTransactions::TYPE_EDIT_POLICY;
@@ -80,217 +65,6 @@
     return $types;
   }
 
-  protected function getCustomTransactionOldValue(
-    PhabricatorLiskDAO $object,
-    PhabricatorApplicationTransaction $xaction) {
-    switch ($xaction->getTransactionType()) {
-      case PhabricatorCalendarEventTransaction::TYPE_RECURRING:
-        return (int)$object->getIsRecurring();
-      case PhabricatorCalendarEventTransaction::TYPE_FREQUENCY:
-        return $object->getFrequencyUnit();
-      case PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE:
-        return $object->getRecurrenceEndDate();
-      case PhabricatorCalendarEventTransaction::TYPE_NAME:
-        return $object->getName();
-      case PhabricatorCalendarEventTransaction::TYPE_START_DATE:
-        return $object->getDateFrom();
-      case PhabricatorCalendarEventTransaction::TYPE_END_DATE:
-        return $object->getDateTo();
-      case PhabricatorCalendarEventTransaction::TYPE_DESCRIPTION:
-        return $object->getDescription();
-      case PhabricatorCalendarEventTransaction::TYPE_CANCEL:
-        return $object->getIsCancelled();
-      case PhabricatorCalendarEventTransaction::TYPE_ALL_DAY:
-        return (int)$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:
-        $invitees = $object->getInvitees();
-        return mpull($invitees, 'getStatus', 'getInviteePHID');
-    }
-
-    return parent::getCustomTransactionOldValue($object, $xaction);
-  }
-
-  protected function getCustomTransactionNewValue(
-    PhabricatorLiskDAO $object,
-    PhabricatorApplicationTransaction $xaction) {
-    switch ($xaction->getTransactionType()) {
-      case PhabricatorCalendarEventTransaction::TYPE_FREQUENCY:
-      case PhabricatorCalendarEventTransaction::TYPE_NAME:
-      case PhabricatorCalendarEventTransaction::TYPE_DESCRIPTION:
-      case PhabricatorCalendarEventTransaction::TYPE_CANCEL:
-      case PhabricatorCalendarEventTransaction::TYPE_ICON:
-        return $xaction->getNewValue();
-      case PhabricatorCalendarEventTransaction::TYPE_ACCEPT:
-        return PhabricatorCalendarEventInvitee::STATUS_ATTENDING;
-      case PhabricatorCalendarEventTransaction::TYPE_DECLINE:
-        return PhabricatorCalendarEventInvitee::STATUS_DECLINED;
-      case PhabricatorCalendarEventTransaction::TYPE_ALL_DAY:
-      case PhabricatorCalendarEventTransaction::TYPE_RECURRING:
-        return (int)$xaction->getNewValue();
-      case PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE:
-      case PhabricatorCalendarEventTransaction::TYPE_START_DATE:
-      case PhabricatorCalendarEventTransaction::TYPE_END_DATE:
-        return $xaction->getNewValue()->getEpoch();
-      case PhabricatorCalendarEventTransaction::TYPE_INVITE:
-        $status_invited = PhabricatorCalendarEventInvitee::STATUS_INVITED;
-        $status_uninvited = PhabricatorCalendarEventInvitee::STATUS_UNINVITED;
-        $status_attending = PhabricatorCalendarEventInvitee::STATUS_ATTENDING;
-
-        $invitees = $object->getInvitees();
-        foreach ($invitees as $key => $invitee) {
-          if ($invitee->getStatus() == $status_uninvited) {
-            unset($invitees[$key]);
-          }
-        }
-        $invitees = mpull($invitees, null, 'getInviteePHID');
-
-        $new = $xaction->getNewValue();
-        $new = array_fuse($new);
-
-        $all = array_keys($invitees + $new);
-        $map = array();
-        foreach ($all as $phid) {
-          $is_old = isset($invitees[$phid]);
-          $is_new = isset($new[$phid]);
-
-          if ($is_old && !$is_new) {
-            $map[$phid] = $status_uninvited;
-          } else if (!$is_old && $is_new) {
-            $map[$phid] = $status_invited;
-          } else {
-            $map[$phid] = $invitees[$phid]->getStatus();
-          }
-        }
-
-        // If we're creating this event and the actor is inviting themselves,
-        // mark them as attending.
-        if ($this->getIsNewObject()) {
-          $acting_phid = $this->getActingAsPHID();
-          if (isset($map[$acting_phid])) {
-            $map[$acting_phid] = $status_attending;
-          }
-        }
-
-        return $map;
-    }
-
-    return parent::getCustomTransactionNewValue($object, $xaction);
-  }
-
-  protected function applyCustomInternalTransaction(
-    PhabricatorLiskDAO $object,
-    PhabricatorApplicationTransaction $xaction) {
-
-    switch ($xaction->getTransactionType()) {
-      case PhabricatorCalendarEventTransaction::TYPE_RECURRING:
-        return $object->setIsRecurring((int)$xaction->getNewValue());
-      case PhabricatorCalendarEventTransaction::TYPE_FREQUENCY:
-        return $object->setRecurrenceFrequency(
-          array(
-            'rule' => $xaction->getNewValue(),
-          ));
-      case PhabricatorCalendarEventTransaction::TYPE_NAME:
-        $object->setName($xaction->getNewValue());
-        return;
-      case PhabricatorCalendarEventTransaction::TYPE_START_DATE:
-        $object->setDateFrom($xaction->getNewValue());
-        return;
-      case PhabricatorCalendarEventTransaction::TYPE_END_DATE:
-        $object->setDateTo($xaction->getNewValue());
-        return;
-      case PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE:
-        $object->setRecurrenceEndDate($xaction->getNewValue());
-        return;
-      case PhabricatorCalendarEventTransaction::TYPE_DESCRIPTION:
-        $object->setDescription($xaction->getNewValue());
-        return;
-      case PhabricatorCalendarEventTransaction::TYPE_CANCEL:
-        $object->setIsCancelled((int)$xaction->getNewValue());
-        return;
-      case PhabricatorCalendarEventTransaction::TYPE_ALL_DAY:
-        $object->setIsAllDay((int)$xaction->getNewValue());
-        return;
-      case PhabricatorCalendarEventTransaction::TYPE_ICON:
-        $object->setIcon($xaction->getNewValue());
-        return;
-      case PhabricatorCalendarEventTransaction::TYPE_INVITE:
-      case PhabricatorCalendarEventTransaction::TYPE_ACCEPT:
-      case PhabricatorCalendarEventTransaction::TYPE_DECLINE:
-        return;
-    }
-
-    return parent::applyCustomInternalTransaction($object, $xaction);
-  }
-
-  protected function applyCustomExternalTransaction(
-    PhabricatorLiskDAO $object,
-    PhabricatorApplicationTransaction $xaction) {
-
-    switch ($xaction->getTransactionType()) {
-      case PhabricatorCalendarEventTransaction::TYPE_RECURRING:
-      case PhabricatorCalendarEventTransaction::TYPE_FREQUENCY:
-      case PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE:
-      case PhabricatorCalendarEventTransaction::TYPE_NAME:
-      case PhabricatorCalendarEventTransaction::TYPE_START_DATE:
-      case PhabricatorCalendarEventTransaction::TYPE_END_DATE:
-      case PhabricatorCalendarEventTransaction::TYPE_DESCRIPTION:
-      case PhabricatorCalendarEventTransaction::TYPE_CANCEL:
-      case PhabricatorCalendarEventTransaction::TYPE_ALL_DAY:
-      case PhabricatorCalendarEventTransaction::TYPE_ICON:
-        return;
-      case PhabricatorCalendarEventTransaction::TYPE_INVITE:
-        $map = $xaction->getNewValue();
-        $phids = array_keys($map);
-        $invitees = $object->getInvitees();
-        $invitees = mpull($invitees, null, 'getInviteePHID');
-
-        foreach ($phids as $phid) {
-          $invitee = idx($invitees, $phid);
-          if (!$invitee) {
-            $invitee = id(new PhabricatorCalendarEventInvitee())
-              ->setEventPHID($object->getPHID())
-              ->setInviteePHID($phid)
-              ->setInviterPHID($this->getActingAsPHID());
-            $invitees[] = $invitee;
-          }
-          $invitee->setStatus($map[$phid])
-            ->save();
-        }
-        $object->attachInvitees($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);
-  }
-
   protected function applyFinalEffects(
     PhabricatorLiskDAO $object,
     array $xactions) {
@@ -302,26 +76,21 @@
     $invalidate_phids = array();
     foreach ($xactions as $xaction) {
       switch ($xaction->getTransactionType()) {
-        case PhabricatorCalendarEventTransaction::TYPE_ICON:
-          break;
-        case PhabricatorCalendarEventTransaction::TYPE_RECURRING:
-        case PhabricatorCalendarEventTransaction::TYPE_FREQUENCY:
-        case PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE:
-        case PhabricatorCalendarEventTransaction::TYPE_START_DATE:
-        case PhabricatorCalendarEventTransaction::TYPE_END_DATE:
-        case PhabricatorCalendarEventTransaction::TYPE_CANCEL:
-        case PhabricatorCalendarEventTransaction::TYPE_ALL_DAY:
+        case PhabricatorCalendarEventUntilDateTransaction::TRANSACTIONTYPE:
+        case PhabricatorCalendarEventStartDateTransaction::TRANSACTIONTYPE:
+        case PhabricatorCalendarEventEndDateTransaction::TRANSACTIONTYPE:
+        case PhabricatorCalendarEventCancelTransaction::TRANSACTIONTYPE:
+        case PhabricatorCalendarEventAllDayTransaction::TRANSACTIONTYPE:
           // For these kinds of changes, we need to invalidate the availabilty
           // caches for all attendees.
           $invalidate_all = true;
           break;
-
-        case PhabricatorCalendarEventTransaction::TYPE_ACCEPT:
-        case PhabricatorCalendarEventTransaction::TYPE_DECLINE:
+        case PhabricatorCalendarEventAcceptTransaction::TRANSACTIONTYPE:
+        case PhabricatorCalendarEventDeclineTransaction::TRANSACTIONTYPE:
           $acting_phid = $this->getActingAsPHID();
           $invalidate_phids[$acting_phid] = $acting_phid;
           break;
-        case PhabricatorCalendarEventTransaction::TYPE_INVITE:
+        case PhabricatorCalendarEventInviteTransaction::TRANSACTIONTYPE:
           foreach ($xaction->getNewValue() as $phid => $ignored) {
             $invalidate_phids[$phid] = $phid;
           }
@@ -357,14 +126,15 @@
   protected function validateAllTransactions(
     PhabricatorLiskDAO $object,
     array $xactions) {
+
     $start_date_xaction =
-      PhabricatorCalendarEventTransaction::TYPE_START_DATE;
+      PhabricatorCalendarEventStartDateTransaction::TRANSACTIONTYPE;
     $end_date_xaction =
-      PhabricatorCalendarEventTransaction::TYPE_END_DATE;
+      PhabricatorCalendarEventEndDateTransaction::TRANSACTIONTYPE;
     $is_recurrence_xaction =
-      PhabricatorCalendarEventTransaction::TYPE_RECURRING;
+      PhabricatorCalendarEventRecurringTransaction::TRANSACTIONTYPE;
     $recurrence_end_xaction =
-      PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE;
+      PhabricatorCalendarEventUntilDateTransaction::TRANSACTIONTYPE;
 
     $start_date = $object->getDateFrom();
     $end_date = $object->getDateTo();
@@ -386,19 +156,16 @@
     }
 
     if ($start_date > $end_date) {
-      $type = PhabricatorCalendarEventTransaction::TYPE_END_DATE;
       $errors[] = new PhabricatorApplicationTransactionValidationError(
-        $type,
+        $end_date_xaction,
         pht('Invalid'),
         pht('End date must be after start date.'),
         null);
     }
 
     if ($recurrence_end && !$is_recurring) {
-      $type =
-        PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE;
       $errors[] = new PhabricatorApplicationTransactionValidationError(
-        $type,
+        $recurrence_end_xaction,
         pht('Invalid'),
         pht('Event must be recurring to have a recurrence end date.').
         null);
@@ -407,97 +174,6 @@
     return $errors;
   }
 
-  protected function validateTransaction(
-    PhabricatorLiskDAO $object,
-    $type,
-    array $xactions) {
-
-    $errors = parent::validateTransaction($object, $type, $xactions);
-
-    switch ($type) {
-      case PhabricatorCalendarEventTransaction::TYPE_NAME:
-        $missing = $this->validateIsEmptyTextField(
-          $object->getName(),
-          $xactions);
-
-        if ($missing) {
-          $error = new PhabricatorApplicationTransactionValidationError(
-            $type,
-            pht('Required'),
-            pht('Event name is required.'),
-            nonempty(last($xactions), null));
-
-          $error->setIsMissingFieldError(true);
-          $errors[] = $error;
-        }
-        break;
-      case PhabricatorCalendarEventTransaction::TYPE_INVITE:
-        $old = $object->getInvitees();
-        $old = mpull($old, null, 'getInviteePHID');
-        foreach ($xactions as $xaction) {
-          $new = $xaction->getNewValue();
-          $new = array_fuse($new);
-          $add = array_diff_key($new, $old);
-          if (!$add) {
-            continue;
-          }
-
-          // In the UI, we only allow you to invite mailable objects, but there
-          // is no definitive marker for "invitable object" today. Just allow
-          // any valid object to be invited.
-          $objects = id(new PhabricatorObjectQuery())
-            ->setViewer($this->getActor())
-            ->withPHIDs($add)
-            ->execute();
-          $objects = mpull($objects, null, 'getPHID');
-          foreach ($add as $phid) {
-            if (isset($objects[$phid])) {
-              continue;
-            }
-
-            $errors[] = new PhabricatorApplicationTransactionValidationError(
-              $type,
-              pht('Invalid'),
-              pht(
-                'Invitee "%s" identifies an object that does not exist or '.
-                'which you do not have permission to view.',
-                $phid));
-          }
-        }
-        break;
-      case PhabricatorCalendarEventTransaction::TYPE_START_DATE:
-      case PhabricatorCalendarEventTransaction::TYPE_END_DATE:
-      case PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE:
-        foreach ($xactions as $xaction) {
-          if ($xaction->getNewValue()->isValid()) {
-            continue;
-          }
-
-          switch ($type) {
-            case PhabricatorCalendarEventTransaction::TYPE_START_DATE:
-              $message = pht('Start date is invalid.');
-              break;
-            case PhabricatorCalendarEventTransaction::TYPE_END_DATE:
-              $message = pht('End date is invalid.');
-              break;
-            case PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE:
-              $message = pht('Repeat until date is invalid.');
-              break;
-          }
-
-          $errors[] = new PhabricatorApplicationTransactionValidationError(
-            $type,
-            pht('Invalid'),
-            $message,
-            $xaction);
-        }
-        break;
-
-    }
-
-    return $errors;
-  }
-
   protected function shouldPublishFeedStory(
     PhabricatorLiskDAO $object,
     array $xactions) {
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
@@ -1,22 +1,7 @@
 <?php
 
 final class PhabricatorCalendarEventTransaction
-  extends PhabricatorApplicationTransaction {
-
-  const TYPE_NAME = 'calendar.name';
-  const TYPE_START_DATE = 'calendar.startdate';
-  const TYPE_END_DATE = 'calendar.enddate';
-  const TYPE_DESCRIPTION = 'calendar.description';
-  const TYPE_CANCEL = 'calendar.cancel';
-  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';
+  extends PhabricatorModularTransaction {
 
   const MAILTAG_RESCHEDULE = 'calendar-reschedule';
   const MAILTAG_CONTENT = 'calendar-content';
@@ -34,580 +19,25 @@
     return new PhabricatorCalendarEventTransactionComment();
   }
 
-  public function getRequiredHandlePHIDs() {
-    $phids = parent::getRequiredHandlePHIDs();
-
-    switch ($this->getTransactionType()) {
-      case self::TYPE_NAME:
-      case self::TYPE_START_DATE:
-      case self::TYPE_END_DATE:
-      case self::TYPE_DESCRIPTION:
-      case self::TYPE_CANCEL:
-      case self::TYPE_ALL_DAY:
-      case self::TYPE_RECURRING:
-      case self::TYPE_FREQUENCY:
-      case self::TYPE_RECURRENCE_END_DATE:
-        $phids[] = $this->getObjectPHID();
-        break;
-      case self::TYPE_INVITE:
-        $new = $this->getNewValue();
-        foreach ($new as $phid => $status) {
-          $phids[] = $phid;
-        }
-        break;
-    }
-
-    return $phids;
-  }
-
-  public function shouldHide() {
-    $old = $this->getOldValue();
-    switch ($this->getTransactionType()) {
-      case self::TYPE_START_DATE:
-      case self::TYPE_END_DATE:
-      case self::TYPE_DESCRIPTION:
-      case self::TYPE_CANCEL:
-      case self::TYPE_ALL_DAY:
-      case self::TYPE_INVITE:
-      case self::TYPE_RECURRING:
-      case self::TYPE_FREQUENCY:
-      case self::TYPE_RECURRENCE_END_DATE:
-        return ($old === null);
-    }
-    return parent::shouldHide();
-  }
-
-  public function getIcon() {
-    switch ($this->getTransactionType()) {
-      case self::TYPE_ICON:
-        return $this->getNewValue();
-      case self::TYPE_NAME:
-      case self::TYPE_START_DATE:
-      case self::TYPE_END_DATE:
-      case self::TYPE_DESCRIPTION:
-      case self::TYPE_ALL_DAY:
-      case self::TYPE_CANCEL:
-      case self::TYPE_RECURRING:
-      case self::TYPE_FREQUENCY:
-      case self::TYPE_RECURRENCE_END_DATE:
-        return 'fa-pencil';
-        break;
-      case self::TYPE_INVITE:
-        return 'fa-user-plus';
-        break;
-    }
-    return parent::getIcon();
-  }
-
-  public function getTitle() {
-    $author_phid = $this->getAuthorPHID();
-    $object_phid = $this->getObjectPHID();
-
-    $old = $this->getOldValue();
-    $new = $this->getNewValue();
-
-    $type = $this->getTransactionType();
-    switch ($type) {
-      case self::TYPE_NAME:
-        if ($old === null) {
-          return pht(
-            '%s created this event.',
-            $this->renderHandleLink($author_phid));
-        } else {
-          return pht(
-            '%s changed the name of this event from %s to %s.',
-            $this->renderHandleLink($author_phid),
-            $old,
-            $new);
-        }
-      case self::TYPE_START_DATE:
-        if ($old) {
-          return pht(
-            '%s edited the start date of this event.',
-            $this->renderHandleLink($author_phid));
-        }
-        break;
-      case self::TYPE_END_DATE:
-        if ($old) {
-          return pht(
-            '%s edited the end date of this event.',
-            $this->renderHandleLink($author_phid));
-        }
-        break;
-      case self::TYPE_DESCRIPTION:
-        return pht(
-          "%s updated the event's description.",
-          $this->renderHandleLink($author_phid));
-      case self::TYPE_ALL_DAY:
-        if ($new) {
-          return pht(
-            '%s made this an all day event.',
-            $this->renderHandleLink($author_phid));
-        } else {
-          return pht(
-            '%s converted this from an all day event.',
-            $this->renderHandleLink($author_phid));
-        }
-      case self::TYPE_ICON:
-        $set = new PhabricatorCalendarIconSet();
-        return pht(
-          '%s set this event\'s icon to %s.',
-          $this->renderHandleLink($author_phid),
-          $set->getIconLabel($new));
-        break;
-      case self::TYPE_CANCEL:
-        if ($new) {
-          return pht(
-            '%s cancelled this event.',
-            $this->renderHandleLink($author_phid));
-        } else {
-          return pht(
-            '%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:
-        $text = null;
-
-        list($old, $new) = $this->getSimpleInvites($old, $new);
-
-        if (count($old) === 1
-          && count($new) === 1
-          && isset($old[$author_phid])) {
-          // user joined/declined/accepted event themself
-          $old_status = $old[$author_phid];
-          $new_status = $new[$author_phid];
-
-          if ($old_status !== $new_status) {
-            switch ($new_status) {
-              case PhabricatorCalendarEventInvitee::STATUS_INVITED:
-                $text = pht(
-                  '%s has joined this event.',
-                  $this->renderHandleLink($author_phid));
-                  break;
-              case PhabricatorCalendarEventInvitee::STATUS_ATTENDING:
-                $text = pht(
-                  '%s is attending this event.',
-                  $this->renderHandleLink($author_phid));
-                  break;
-              case PhabricatorCalendarEventInvitee::STATUS_DECLINED:
-              case PhabricatorCalendarEventInvitee::STATUS_UNINVITED:
-                $text = pht(
-                  '%s has declined this event.',
-                  $this->renderHandleLink($author_phid));
-                  break;
-              default:
-                $text = pht(
-                  '%s has changed their status for this event.',
-                  $this->renderHandleLink($author_phid));
-                break;
-            }
-          }
-        } else {
-          // user changed status for many users
-          $self_joined = null;
-          $self_declined = null;
-          $added = array();
-          $uninvited = array();
-
-          foreach ($new as $phid => $status) {
-            if ($status == PhabricatorCalendarEventInvitee::STATUS_INVITED
-              || $status == PhabricatorCalendarEventInvitee::STATUS_ATTENDING) {
-              // added users
-              $added[] = $phid;
-            } else if (
-              $status == PhabricatorCalendarEventInvitee::STATUS_DECLINED
-              || $status == PhabricatorCalendarEventInvitee::STATUS_UNINVITED) {
-              $uninvited[] = $phid;
-            }
-          }
-
-          $count_added = count($added);
-          $count_uninvited = count($uninvited);
-          $added_text = null;
-          $uninvited_text = null;
-
-          if ($count_added > 0 && $count_uninvited == 0) {
-            $added_text = $this->renderHandleList($added);
-            $text = pht('%s invited %s.',
-              $this->renderHandleLink($author_phid),
-              $added_text);
-          } else if ($count_added > 0 && $count_uninvited > 0) {
-            $added_text = $this->renderHandleList($added);
-            $uninvited_text = $this->renderHandleList($uninvited);
-            $text = pht('%s invited %s and uninvited %s.',
-              $this->renderHandleLink($author_phid),
-              $added_text,
-              $uninvited_text);
-          } else if ($count_added == 0 && $count_uninvited > 0) {
-            $uninvited_text = $this->renderHandleList($uninvited);
-            $text = pht('%s uninvited %s.',
-              $this->renderHandleLink($author_phid),
-              $uninvited_text);
-          } else {
-            $text = pht('%s updated the invitee list.',
-              $this->renderHandleLink($author_phid));
-          }
-        }
-        return $text;
-      case self::TYPE_RECURRING:
-        $text = pht('%s made this event recurring.',
-          $this->renderHandleLink($author_phid));
-        return $text;
-      case self::TYPE_FREQUENCY:
-        $rule = $new;
-        if (is_array($rule)) {
-          $rule = idx($rule, 'rule');
-        }
-
-        $text = '';
-        switch ($rule) {
-          case PhabricatorCalendarEvent::FREQUENCY_DAILY:
-            $text = pht('%s set this event to repeat daily.',
-              $this->renderHandleLink($author_phid));
-            break;
-          case PhabricatorCalendarEvent::FREQUENCY_WEEKLY:
-            $text = pht('%s set this event to repeat weekly.',
-              $this->renderHandleLink($author_phid));
-            break;
-          case PhabricatorCalendarEvent::FREQUENCY_MONTHLY:
-            $text = pht('%s set this event to repeat monthly.',
-              $this->renderHandleLink($author_phid));
-            break;
-          case PhabricatorCalendarEvent::FREQUENCY_YEARLY:
-            $text = pht('%s set this event to repeat yearly.',
-              $this->renderHandleLink($author_phid));
-            break;
-        }
-        return $text;
-      case self::TYPE_RECURRENCE_END_DATE:
-        $text = pht('%s has changed the recurrence end date of this event.',
-          $this->renderHandleLink($author_phid));
-        return $text;
-    }
-    return parent::getTitle();
-  }
-
-  public function getTitleForFeed() {
-    $author_phid = $this->getAuthorPHID();
-    $object_phid = $this->getObjectPHID();
-
-    $old = $this->getOldValue();
-    $new = $this->getNewValue();
-
-    $viewer = $this->getViewer();
-
-    $type = $this->getTransactionType();
-    switch ($type) {
-      case self::TYPE_NAME:
-        if ($old === null) {
-          return pht(
-            '%s created %s.',
-            $this->renderHandleLink($author_phid),
-            $this->renderHandleLink($object_phid));
-        } else {
-          return pht(
-            '%s changed the name of %s from %s to %s.',
-            $this->renderHandleLink($author_phid),
-            $this->renderHandleLink($object_phid),
-            $old,
-            $new);
-        }
-      case self::TYPE_START_DATE:
-        if ($old) {
-          $old = phabricator_datetime($old, $viewer);
-          $new = phabricator_datetime($new, $viewer);
-          return pht(
-            '%s changed the start date of %s from %s to %s.',
-            $this->renderHandleLink($author_phid),
-            $this->renderHandleLink($object_phid),
-            $old,
-            $new);
-        }
-        break;
-      case self::TYPE_END_DATE:
-        if ($old) {
-          $old = phabricator_datetime($old, $viewer);
-          $new = phabricator_datetime($new, $viewer);
-          return pht(
-            '%s edited the end date of %s from %s to %s.',
-            $this->renderHandleLink($author_phid),
-            $this->renderHandleLink($object_phid),
-            $old,
-            $new);
-        }
-        break;
-      case self::TYPE_DESCRIPTION:
-        return pht(
-          '%s updated the description of %s.',
-          $this->renderHandleLink($author_phid),
-          $this->renderHandleLink($object_phid));
-      case self::TYPE_ALL_DAY:
-        if ($new) {
-          return pht(
-            '%s made %s an all day event.',
-            $this->renderHandleLink($author_phid),
-            $this->renderHandleLink($object_phid));
-        } else {
-          return pht(
-            '%s converted %s from an all day event.',
-            $this->renderHandleLink($author_phid),
-            $this->renderHandleLink($object_phid));
-        }
-      case self::TYPE_ICON:
-        $set = new PhabricatorCalendarIconSet();
-        return pht(
-          '%s set the icon for %s to %s.',
-          $this->renderHandleLink($author_phid),
-          $this->renderHandleLink($object_phid),
-          $set->getIconLabel($new));
-      case self::TYPE_CANCEL:
-        if ($new) {
-          return pht(
-            '%s cancelled %s.',
-            $this->renderHandleLink($author_phid),
-            $this->renderHandleLink($object_phid));
-        } else {
-          return pht(
-            '%s reinstated %s.',
-            $this->renderHandleLink($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:
-        $text = null;
-
-        list($old, $new) = $this->getSimpleInvites($old, $new);
-
-        if (count($old) === 1
-          && count($new) === 1
-          && isset($old[$author_phid])) {
-          // user joined/declined/accepted event themself
-          $old_status = $old[$author_phid];
-          $new_status = $new[$author_phid];
-
-          if ($old_status !== $new_status) {
-            switch ($new_status) {
-              case PhabricatorCalendarEventInvitee::STATUS_INVITED:
-                $text = pht(
-                  '%s has joined %s.',
-                  $this->renderHandleLink($author_phid),
-                  $this->renderHandleLink($object_phid));
-                  break;
-              case PhabricatorCalendarEventInvitee::STATUS_ATTENDING:
-                $text = pht(
-                  '%s is attending %s.',
-                  $this->renderHandleLink($author_phid),
-                  $this->renderHandleLink($object_phid));
-                  break;
-              case PhabricatorCalendarEventInvitee::STATUS_DECLINED:
-              case PhabricatorCalendarEventInvitee::STATUS_UNINVITED:
-                $text = pht(
-                  '%s has declined %s.',
-                  $this->renderHandleLink($author_phid),
-                  $this->renderHandleLink($object_phid));
-                  break;
-              default:
-                $text = pht(
-                  '%s has changed their status of %s.',
-                  $this->renderHandleLink($author_phid),
-                  $this->renderHandleLink($object_phid));
-                break;
-            }
-          }
-        } else {
-          // user changed status for many users
-          $self_joined = null;
-          $self_declined = null;
-          $added = array();
-          $uninvited = array();
-
-          foreach ($new as $phid => $status) {
-            if ($status == PhabricatorCalendarEventInvitee::STATUS_INVITED
-              || $status == PhabricatorCalendarEventInvitee::STATUS_ATTENDING) {
-              // added users
-              $added[] = $phid;
-            } else if (
-              $status == PhabricatorCalendarEventInvitee::STATUS_DECLINED
-              || $status == PhabricatorCalendarEventInvitee::STATUS_UNINVITED) {
-              $uninvited[] = $phid;
-            }
-          }
-
-          $count_added = count($added);
-          $count_uninvited = count($uninvited);
-          $added_text = null;
-          $uninvited_text = null;
-
-          if ($count_added > 0 && $count_uninvited == 0) {
-            $added_text = $this->renderHandleList($added);
-            $text = pht('%s invited %s to %s.',
-              $this->renderHandleLink($author_phid),
-              $added_text,
-              $this->renderHandleLink($object_phid));
-          } else if ($count_added > 0 && $count_uninvited > 0) {
-            $added_text = $this->renderHandleList($added);
-            $uninvited_text = $this->renderHandleList($uninvited);
-            $text = pht('%s invited %s and uninvited %s to %s.',
-              $this->renderHandleLink($author_phid),
-              $added_text,
-              $uninvited_text,
-              $this->renderHandleLink($object_phid));
-          } else if ($count_added == 0 && $count_uninvited > 0) {
-            $uninvited_text = $this->renderHandleList($uninvited);
-            $text = pht('%s uninvited %s to %s.',
-              $this->renderHandleLink($author_phid),
-              $uninvited_text,
-              $this->renderHandleLink($object_phid));
-          } else {
-            $text = pht('%s updated the invitee list of %s.',
-              $this->renderHandleLink($author_phid),
-              $this->renderHandleLink($object_phid));
-          }
-        }
-        return $text;
-      case self::TYPE_RECURRING:
-        $text = pht('%s made %s a recurring event.',
-          $this->renderHandleLink($author_phid),
-          $this->renderHandleLink($object_phid));
-        return $text;
-      case self::TYPE_FREQUENCY:
-        $rule = $new;
-        if (is_array($rule)) {
-          $rule = idx($rule, 'rule');
-        }
-
-        $text = '';
-        switch ($rule) {
-          case PhabricatorCalendarEvent::FREQUENCY_DAILY:
-            $text = pht('%s set %s to repeat daily.',
-              $this->renderHandleLink($author_phid),
-              $this->renderHandleLink($object_phid));
-            break;
-          case PhabricatorCalendarEvent::FREQUENCY_WEEKLY:
-            $text = pht('%s set %s to repeat weekly.',
-              $this->renderHandleLink($author_phid),
-              $this->renderHandleLink($object_phid));
-            break;
-          case PhabricatorCalendarEvent::FREQUENCY_MONTHLY:
-            $text = pht('%s set %s to repeat monthly.',
-              $this->renderHandleLink($author_phid),
-              $this->renderHandleLink($object_phid));
-            break;
-          case PhabricatorCalendarEvent::FREQUENCY_YEARLY:
-            $text = pht('%s set %s to repeat yearly.',
-              $this->renderHandleLink($author_phid),
-              $this->renderHandleLink($object_phid));
-            break;
-        }
-        return $text;
-      case self::TYPE_RECURRENCE_END_DATE:
-        $text = pht('%s set the recurrence end date of %s to %s.',
-          $this->renderHandleLink($author_phid),
-          $this->renderHandleLink($object_phid),
-          $new);
-        return $text;
-    }
-
-    return parent::getTitleForFeed();
-  }
-
-  public function getColor() {
-    $old = $this->getOldValue();
-    $new = $this->getNewValue();
-
-    switch ($this->getTransactionType()) {
-      case self::TYPE_NAME:
-      case self::TYPE_START_DATE:
-      case self::TYPE_END_DATE:
-      case self::TYPE_DESCRIPTION:
-      case self::TYPE_CANCEL:
-      case self::TYPE_INVITE:
-        return PhabricatorTransactions::COLOR_GREEN;
-    }
-
-    return parent::getColor();
-  }
-
-
-  public function hasChangeDetails() {
-    switch ($this->getTransactionType()) {
-      case self::TYPE_DESCRIPTION:
-        return ($this->getOldValue() !== null);
-    }
-
-    return parent::hasChangeDetails();
-  }
-
-  public function renderChangeDetails(PhabricatorUser $viewer) {
-    switch ($this->getTransactionType()) {
-      case self::TYPE_DESCRIPTION:
-        $old = $this->getOldValue();
-        $new = $this->getNewValue();
-
-        return $this->renderTextCorpusChangeDetails(
-          $viewer,
-          $old,
-          $new);
-    }
-
-    return parent::renderChangeDetails($viewer);
+  public function getBaseTransactionClass() {
+    return 'PhabricatorCalendarEventTransactionType';
   }
 
   public function getMailTags() {
     $tags = array();
     switch ($this->getTransactionType()) {
-      case self::TYPE_NAME:
-      case self::TYPE_DESCRIPTION:
-      case self::TYPE_INVITE:
-      case self::TYPE_ICON:
+      case PhabricatorCalendarEventNameTransaction::TRANSACTIONTYPE:
+      case PhabricatorCalendarEventDescriptionTransaction::TRANSACTIONTYPE:
+      case PhabricatorCalendarEventInviteTransaction::TRANSACTIONTYPE:
         $tags[] = self::MAILTAG_CONTENT;
         break;
-      case self::TYPE_START_DATE:
-      case self::TYPE_END_DATE:
-      case self::TYPE_CANCEL:
+      case PhabricatorCalendarEventStartDateTransaction::TRANSACTIONTYPE:
+      case PhabricatorCalendarEventEndDateTransaction::TRANSACTIONTYPE:
+      case PhabricatorCalendarEventCancelTransaction::TRANSACTIONTYPE:
         $tags[] = self::MAILTAG_RESCHEDULE;
         break;
     }
     return $tags;
   }
 
-  private function getSimpleInvites(array $old, array $new) {
-    // Fill in any new invitees as "uninvited" in the old data, to make
-    // some of the rendering logic a little easier.
-    $status_uninvited = PhabricatorCalendarEventInvitee::STATUS_UNINVITED;
-    $old = $old + array_fill_keys(array_keys($new), $status_uninvited);
-
-    $all = $old + $new;
-    foreach (array_keys($all) as $key) {
-      // If the invitee exists in both the old and new lists with the same
-      // value, remove it from both.
-      if (isset($old[$key]) && isset($new[$key])) {
-        if ($old[$key] == $new[$key]) {
-          unset($old[$key]);
-          unset($new[$key]);
-        }
-      }
-    }
-
-    return array($old, $new);
-  }
-
-
 }
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventAcceptTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventAcceptTransaction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventAcceptTransaction.php
@@ -0,0 +1,25 @@
+<?php
+
+final class PhabricatorCalendarEventAcceptTransaction
+  extends PhabricatorCalendarEventReplyTransaction {
+
+  const TRANSACTIONTYPE = 'calendar.accept';
+
+  public function generateNewValue($object, $value) {
+    return PhabricatorCalendarEventInvitee::STATUS_ATTENDING;
+  }
+
+  public function getTitle() {
+    return pht(
+      '%s is attending this event.',
+      $this->renderAuthor());
+  }
+
+  public function getTitleForFeed() {
+    return pht(
+      '%s is attending %s.',
+      $this->renderAuthor(),
+      $this->renderObject());
+  }
+
+}
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventAllDayTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventAllDayTransaction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventAllDayTransaction.php
@@ -0,0 +1,46 @@
+<?php
+
+final class PhabricatorCalendarEventAllDayTransaction
+  extends PhabricatorCalendarEventTransactionType {
+
+  const TRANSACTIONTYPE = 'calendar.allday';
+
+  public function generateOldValue($object) {
+    return (int)$object->getIsAllDay();
+  }
+
+  public function generateNewValue($object, $value) {
+    return (int)$value;
+  }
+
+  public function applyInternalEffects($object, $value) {
+    $object->setIsAllDay($value);
+  }
+
+  public function getTitle() {
+    if ($this->getNewValue()) {
+      return pht(
+        '%s changed this as an all day event.',
+        $this->renderAuthor());
+    } else {
+      return pht(
+        '%s conveted this from an all day event.',
+        $this->renderAuthor());
+    }
+  }
+
+  public function getTitleForFeed() {
+    if ($this->getNewValue()) {
+      return pht(
+        '%s changed %s to an all day event.',
+        $this->renderAuthor(),
+        $this->renderObject());
+    } else {
+      return pht(
+        '%s converted %s from an all day event.',
+        $this->renderAuthor(),
+        $this->renderObject());
+    }
+  }
+
+}
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventCancelTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventCancelTransaction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventCancelTransaction.php
@@ -0,0 +1,46 @@
+<?php
+
+final class PhabricatorCalendarEventCancelTransaction
+  extends PhabricatorCalendarEventTransactionType {
+
+  const TRANSACTIONTYPE = 'calendar.cancel';
+
+  public function generateOldValue($object) {
+    return (int)$object->getIsCancelled();
+  }
+
+  public function generateNewValue($object, $value) {
+    return (int)$value;
+  }
+
+  public function applyInternalEffects($object, $value) {
+    $object->setIsCancelled($value);
+  }
+
+  public function getTitle() {
+    if ($this->getNewValue()) {
+      return pht(
+        '%s cancelled this event.',
+        $this->renderAuthor());
+    } else {
+      return pht(
+        '%s reinstated this event.',
+        $this->renderAuthor());
+    }
+  }
+
+  public function getTitleForFeed() {
+    if ($this->getNewValue()) {
+      return pht(
+        '%s cancelled %s.',
+        $this->renderAuthor(),
+        $this->renderObject());
+    } else {
+      return pht(
+        '%s reinstated %s.',
+        $this->renderAuthor(),
+        $this->renderObject());
+    }
+  }
+
+}
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventDateTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventDateTransaction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventDateTransaction.php
@@ -0,0 +1,27 @@
+<?php
+
+abstract class PhabricatorCalendarEventDateTransaction
+  extends PhabricatorCalendarEventTransactionType {
+
+  abstract protected function getInvalidDateMessage();
+
+  public function generateNewValue($object, $value) {
+    return $value->getEpoch();
+  }
+
+  public function validateTransactions($object, array $xactions) {
+    $errors = array();
+
+    foreach ($xactions as $xaction) {
+      if ($xaction->getNewValue()->isValid()) {
+        continue;
+      }
+
+      $message = $this->getInvalidDateMessage();
+      $errors[] = $this->newInvalidError($message, $xaction);
+    }
+
+    return $errors;
+  }
+
+}
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventDeclineTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventDeclineTransaction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventDeclineTransaction.php
@@ -0,0 +1,25 @@
+<?php
+
+final class PhabricatorCalendarEventDeclineTransaction
+  extends PhabricatorCalendarEventReplyTransaction {
+
+  const TRANSACTIONTYPE = 'calendar.decline';
+
+  public function generateNewValue($object, $value) {
+    return PhabricatorCalendarEventInvitee::STATUS_DECLINED;
+  }
+
+  public function getTitle() {
+    return pht(
+      '%s declined this event.',
+      $this->renderAuthor());
+  }
+
+  public function getTitleForFeed() {
+    return pht(
+      '%s declined %s.',
+      $this->renderAuthor(),
+      $this->renderObject());
+  }
+
+}
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventDescriptionTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventDescriptionTransaction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventDescriptionTransaction.php
@@ -0,0 +1,42 @@
+<?php
+
+final class PhabricatorCalendarEventDescriptionTransaction
+  extends PhabricatorCalendarEventTransactionType {
+
+  const TRANSACTIONTYPE = 'calendar.description';
+
+  public function generateOldValue($object) {
+    return $object->getDescription();
+  }
+
+  public function applyInternalEffects($object, $value) {
+    $object->setDescription($value);
+  }
+
+  public function getTitle() {
+    return pht(
+      '%s updated the event description.',
+      $this->renderAuthor());
+  }
+
+  public function getTitleForFeed() {
+    return pht(
+      '%s updated the event description for %s.',
+      $this->renderAuthor(),
+      $this->renderObject());
+  }
+
+  public function hasChangeDetailView() {
+    return true;
+  }
+
+  public function newChangeDetailView() {
+    $viewer = $this->getViewer();
+
+    return id(new PhabricatorApplicationTransactionTextDiffDetailView())
+      ->setViewer($viewer)
+      ->setOldText($this->getOldValue())
+      ->setNewText($this->getNewValue());
+  }
+
+}
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventEndDateTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventEndDateTransaction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventEndDateTransaction.php
@@ -0,0 +1,37 @@
+<?php
+
+final class PhabricatorCalendarEventEndDateTransaction
+  extends PhabricatorCalendarEventDateTransaction {
+
+  const TRANSACTIONTYPE = 'calendar.enddate';
+
+  public function generateOldValue($object) {
+    return $object->getDateTo();
+  }
+
+  public function applyInternalEffects($object, $value) {
+    $object->setDateTo($value);
+  }
+
+  public function getTitle() {
+    return pht(
+      '%s changed the end date for this event from %s to %s.',
+      $this->renderAuthor(),
+      $this->renderOldDate(),
+      $this->renderNewDate());
+  }
+
+  public function getTitleForFeed() {
+    return pht(
+      '%s changed the end date for %s from %s to %s.',
+      $this->renderAuthor(),
+      $this->renderObject(),
+      $this->renderOldDate(),
+      $this->renderNewDate());
+  }
+
+  protected function getInvalidDateMessage() {
+    return pht('End date is invalid.');
+  }
+
+}
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventFrequencyTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventFrequencyTransaction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventFrequencyTransaction.php
@@ -0,0 +1,75 @@
+<?php
+
+final class PhabricatorCalendarEventFrequencyTransaction
+  extends PhabricatorCalendarEventTransactionType {
+
+  const TRANSACTIONTYPE = 'calendar.frequency';
+
+  public function generateOldValue($object) {
+    return $object->getFrequencyUnit();
+  }
+
+  public function applyInternalEffects($object, $value) {
+    $object->setRecurrenceFrequency(
+      array(
+        'rule' => $value,
+      ));
+  }
+
+  public function getTitle() {
+    $frequency = $this->getFrequencyUnit($this->getNewValue());
+    switch ($frequency) {
+      case PhabricatorCalendarEvent::FREQUENCY_DAILY:
+        return pht(
+          '%s set this event to repeat daily.',
+          $this->renderAuthor());
+      case PhabricatorCalendarEvent::FREQUENCY_WEEKLY:
+        return pht(
+          '%s set this event to repeat weekly.',
+          $this->renderAuthor());
+      case PhabricatorCalendarEvent::FREQUENCY_MONTHLY:
+        return pht(
+          '%s set this event to repeat monthly.',
+          $this->renderAuthor());
+      case PhabricatorCalendarEvent::FREQUENCY_YEARLY:
+        return pht(
+          '%s set this event to repeat yearly.',
+          $this->renderAuthor());
+    }
+  }
+
+  public function getTitleForFeed() {
+    $frequency = $this->getFrequencyUnit($this->getNewValue());
+    switch ($frequency) {
+      case PhabricatorCalendarEvent::FREQUENCY_DAILY:
+        return pht(
+          '%s set %s to repeat daily.',
+          $this->renderAuthor(),
+          $this->renderObject());
+      case PhabricatorCalendarEvent::FREQUENCY_WEEKLY:
+        return pht(
+          '%s set %s to repeat weekly.',
+          $this->renderAuthor(),
+          $this->renderObject());
+      case PhabricatorCalendarEvent::FREQUENCY_MONTHLY:
+        return pht(
+          '%s set %s to repeat monthly.',
+          $this->renderAuthor(),
+          $this->renderObject());
+      case PhabricatorCalendarEvent::FREQUENCY_YEARLY:
+        return pht(
+          '%s set %s to repeat yearly.',
+          $this->renderAuthor(),
+          $this->renderObject());
+    }
+  }
+
+  private function getFrequencyUnit($value) {
+    if (is_array($value)) {
+      $value = idx($value, 'rule');
+    } else {
+      return $value;
+    }
+  }
+
+}
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventIconTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventIconTransaction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventIconTransaction.php
@@ -0,0 +1,44 @@
+<?php
+
+final class PhabricatorCalendarEventIconTransaction
+  extends PhabricatorCalendarEventTransactionType {
+
+  const TRANSACTIONTYPE = 'calendar.icon';
+
+  public function generateOldValue($object) {
+    return $object->getIcon();
+  }
+
+  public function applyInternalEffects($object, $value) {
+    $object->setIcon($value);
+  }
+
+  public function getTitle() {
+    $old = $this->getIconLabel($this->getOldValue());
+    $new = $this->getIconLabel($this->getNewValue());
+
+    return pht(
+      '%s changed the event icon from %s to %s.',
+      $this->renderAuthor(),
+      $this->renderValue($old),
+      $this->renderValue($new));
+  }
+
+  public function getTitleForFeed() {
+    $old = $this->getIconLabel($this->getOldValue());
+    $new = $this->getIconLabel($this->getNewValue());
+
+    return pht(
+      '%s changed the icon for %s from %s to %s.',
+      $this->renderAuthor(),
+      $this->renderObject(),
+      $this->renderValue($old),
+      $this->renderValue($new));
+  }
+
+  private function getIconLabel($icon) {
+    $set = new PhabricatorCalendarIconSet();
+    return $set->getIconLabel($icon);
+  }
+
+}
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventInviteTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventInviteTransaction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventInviteTransaction.php
@@ -0,0 +1,191 @@
+<?php
+
+final class PhabricatorCalendarEventInviteTransaction
+  extends PhabricatorCalendarEventTransactionType {
+
+  const TRANSACTIONTYPE = 'calendar.invite';
+
+  public function generateOldValue($object) {
+    $status_uninvited = PhabricatorCalendarEventInvitee::STATUS_UNINVITED;
+
+    $invitees = $object->getInvitees();
+    foreach ($invitees as $key => $invitee) {
+      if ($invitee->getStatus() == $status_uninvited) {
+        unset($invitees[$key]);
+      }
+    }
+
+    return mpull($invitees, 'getStatus', 'getInviteePHID');
+  }
+
+  public function generateNewValue($object, $value) {
+    $status_invited = PhabricatorCalendarEventInvitee::STATUS_INVITED;
+    $status_uninvited = PhabricatorCalendarEventInvitee::STATUS_UNINVITED;
+    $status_attending = PhabricatorCalendarEventInvitee::STATUS_ATTENDING;
+
+    $invitees = $this->generateOldValue($object);
+
+    $new = array_fuse($value);
+
+    $all = array_keys($invitees + $new);
+    $map = array();
+    foreach ($all as $phid) {
+      $is_old = isset($invitees[$phid]);
+      $is_new = isset($new[$phid]);
+
+      if ($is_old && !$is_new) {
+        $map[$phid] = $status_uninvited;
+      } else if (!$is_old && $is_new) {
+        $map[$phid] = $status_invited;
+      } else {
+        $map[$phid] = $invitees[$phid];
+      }
+    }
+
+    // If we're creating this event and the actor is inviting themselves,
+    // mark them as attending.
+    if ($this->isNewObject()) {
+      $acting_phid = $this->getActingAsPHID();
+      if (isset($map[$acting_phid])) {
+        $map[$acting_phid] = $status_attending;
+      }
+    }
+
+    return $map;
+  }
+
+  public function applyExternalEffects($object, $value) {
+    $phids = array_keys($value);
+    $invitees = $object->getInvitees();
+    $invitees = mpull($invitees, null, 'getInviteePHID');
+
+    foreach ($phids as $phid) {
+      $invitee = idx($invitees, $phid);
+      if (!$invitee) {
+        $invitee = id(new PhabricatorCalendarEventInvitee())
+          ->setEventPHID($object->getPHID())
+          ->setInviteePHID($phid)
+          ->setInviterPHID($this->getActingAsPHID());
+        $invitees[] = $invitee;
+      }
+      $invitee->setStatus($value[$phid])
+        ->save();
+    }
+
+    $object->attachInvitees($invitees);
+  }
+
+  public function validateTransactions($object, array $xactions) {
+    $actor = $this->getActor();
+
+    $errors = array();
+
+    $old = $object->getInvitees();
+    $old = mpull($old, null, 'getInviteePHID');
+    foreach ($xactions as $xaction) {
+      $new = $xaction->getNewValue();
+      $new = array_fuse($new);
+      $add = array_diff_key($new, $old);
+      if (!$add) {
+        continue;
+      }
+
+      // In the UI, we only allow you to invite mailable objects, but there
+      // is no definitive marker for "invitable object" today. Just allow
+      // any valid object to be invited.
+      $objects = id(new PhabricatorObjectQuery())
+        ->setViewer($actor)
+        ->withPHIDs($add)
+        ->execute();
+      $objects = mpull($objects, null, 'getPHID');
+      foreach ($add as $phid) {
+        if (isset($objects[$phid])) {
+          continue;
+        }
+
+        $errors[] = $this->newInvalidError(
+          pht(
+            'Invitee "%s" identifies an object that does not exist or '.
+            'which you do not have permission to view.',
+            $phid),
+          $xaction);
+      }
+    }
+
+    return $errors;
+  }
+
+  public function getIcon() {
+    return 'fa-user-plus';
+  }
+
+  public function getTitle() {
+    list($add, $rem) = $this->getChanges();
+
+    if ($add && !$rem) {
+      return pht(
+        '%s invited %s attendee(s): %s.',
+        $this->renderAuthor(),
+        phutil_count($add),
+        $this->renderHandleList($add));
+    } else if (!$add && $rem) {
+      return pht(
+        '%s uninvited %s attendee(s): %s.',
+        $this->renderAuthor(),
+        phutil_count($rem),
+        $this->renderHandleList($rem));
+    } else {
+      return pht(
+        '%s invited %s attendee(s): %s; uninvinted %s attendee(s): %s.',
+        $this->renderAuthor(),
+        phutil_count($add),
+        $this->renderHandleList($add),
+        phutil_count($rem),
+        $this->renderHandleList($rem));
+    }
+  }
+
+  public function getTitleForFeed() {
+    list($add, $rem) = $this->getChanges();
+
+    if ($add && !$rem) {
+      return pht(
+        '%s invited %s attendee(s) to %s: %s.',
+        $this->renderAuthor(),
+        phutil_count($add),
+        $this->renderObject(),
+        $this->renderHandleList($add));
+    } else if (!$add && $rem) {
+      return pht(
+        '%s uninvited %s attendee(s) to %s: %s.',
+        $this->renderAuthor(),
+        phutil_count($rem),
+        $this->renderObject(),
+        $this->renderHandleList($rem));
+    } else {
+      return pht(
+        '%s updated the invite list for %s, invited %s: %s; '.
+        'uninvinted %s: %s.',
+        $this->renderAuthor(),
+        $this->renderObject(),
+        phutil_count($add),
+        $this->renderHandleList($add),
+        phutil_count($rem),
+        $this->renderHandleList($rem));
+    }
+  }
+
+  private function getChanges() {
+    $old = $this->getOldValue();
+    $new = $this->getNewValue();
+
+    $add = array_diff_key($new, $old);
+    $rem = array_diff_key($old, $new);
+
+    $add = array_keys($add);
+    $rem = array_keys($rem);
+
+    return array(array_fuse($add), array_fuse($rem));
+  }
+
+}
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventNameTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventNameTransaction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventNameTransaction.php
@@ -0,0 +1,44 @@
+<?php
+
+final class PhabricatorCalendarEventNameTransaction
+  extends PhabricatorCalendarEventTransactionType {
+
+  const TRANSACTIONTYPE = 'calendar.name';
+
+  public function generateOldValue($object) {
+    return $object->getName();
+  }
+
+  public function applyInternalEffects($object, $value) {
+    $object->setName($value);
+  }
+
+  public function getTitle() {
+    return pht(
+      '%s renamed this event from %s to %s.',
+      $this->renderAuthor(),
+      $this->renderOldValue(),
+      $this->renderNewValue());
+  }
+
+  public function getTitleForFeed() {
+    return pht(
+      '%s renamed %s from %s to %s.',
+      $this->renderAuthor(),
+      $this->renderObject(),
+      $this->renderOldValue(),
+      $this->renderNewValue());
+  }
+
+  public function validateTransactions($object, array $xactions) {
+    $errors = array();
+
+    if ($this->isEmptyTextTransaction($object->getName(), $xactions)) {
+      $errors[] = $this->newRequiredError(
+        pht('Events must have a name.'));
+    }
+
+    return $errors;
+  }
+
+}
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventRecurringTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventRecurringTransaction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventRecurringTransaction.php
@@ -0,0 +1,44 @@
+<?php
+
+final class PhabricatorCalendarEventRecurringTransaction
+  extends PhabricatorCalendarEventTransactionType {
+
+  const TRANSACTIONTYPE = 'calendar.recurring';
+
+  public function generateOldValue($object) {
+    return (int)$object->getIsRecurring();
+  }
+
+  public function generateNewValue($object, $value) {
+    return (int)$value;
+  }
+
+  public function applyInternalEffects($object, $value) {
+    $object->setIsRecurring($value);
+  }
+
+  public function validateTransactions($object, array $xactions) {
+    $errors = array();
+
+    $old = $object->getIsRecurring();
+    foreach ($xactions as $xaction) {
+      if ($this->getIsNewObject()) {
+        continue;
+      }
+
+      if ($xaction->getNewValue() == $old) {
+        continue;
+      }
+
+      $errors[] = $this->newInvalidError(
+        pht(
+          'An event can only be made recurring when it is created. '.
+          'You can not convert an existing event into a recurring '.
+          'event or vice versa.'),
+        $xaction);
+    }
+
+    return $errors;
+  }
+
+}
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventReplyTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventReplyTransaction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventReplyTransaction.php
@@ -0,0 +1,33 @@
+<?php
+
+abstract class PhabricatorCalendarEventReplyTransaction
+  extends PhabricatorCalendarEventTransactionType {
+
+  public function generateOldValue($object) {
+    $actor_phid = $this->getActingAsPHID();
+    return $object->getUserInviteStatus($actor_phid);
+  }
+
+  public function applyExternalEffects($object, $value) {
+    $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;
+    }
+
+    $invitee
+      ->setStatus($value)
+      ->save();
+
+    $object->attachInvitees($invitees);
+  }
+
+}
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventStartDateTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventStartDateTransaction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventStartDateTransaction.php
@@ -0,0 +1,37 @@
+<?php
+
+final class PhabricatorCalendarEventStartDateTransaction
+  extends PhabricatorCalendarEventDateTransaction {
+
+  const TRANSACTIONTYPE = 'calendar.startdate';
+
+  public function generateOldValue($object) {
+    return $object->getDateFrom();
+  }
+
+  public function applyInternalEffects($object, $value) {
+    $object->setDateFrom($value);
+  }
+
+  public function getTitle() {
+    return pht(
+      '%s changed the start date for this event from %s to %s.',
+      $this->renderAuthor(),
+      $this->renderOldDate(),
+      $this->renderNewDate());
+  }
+
+  public function getTitleForFeed() {
+    return pht(
+      '%s changed the start date for %s from %s to %s.',
+      $this->renderAuthor(),
+      $this->renderObject(),
+      $this->renderOldDate(),
+      $this->renderNewDate());
+  }
+
+  protected function getInvalidDateMessage() {
+    return pht('Start date is invalid.');
+  }
+
+}
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventTransactionType.php b/src/applications/calendar/xaction/PhabricatorCalendarEventTransactionType.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventTransactionType.php
@@ -0,0 +1,4 @@
+<?php
+
+abstract class PhabricatorCalendarEventTransactionType
+  extends PhabricatorModularTransactionType {}
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventUntilDateTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventUntilDateTransaction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventUntilDateTransaction.php
@@ -0,0 +1,35 @@
+<?php
+
+final class PhabricatorCalendarEventUntilDateTransaction
+  extends PhabricatorCalendarEventDateTransaction {
+
+  const TRANSACTIONTYPE = 'calendar.recurrenceenddate';
+
+  public function generateOldValue($object) {
+    return $object->getRecurrenceEndDate();
+  }
+
+  public function applyInternalEffects($object, $value) {
+    $object->setRecurrenceEndDate($value);
+  }
+
+  public function getTitle() {
+    return pht(
+      '%s changed this event to repeat until %s.',
+      $this->renderAuthor(),
+      $this->renderNewDate());
+  }
+
+  public function getTitleForFeed() {
+    return pht(
+      '%s changed %s to repeat until %s.',
+      $this->renderAuthor(),
+      $this->renderObject(),
+      $this->renderNewDate());
+  }
+
+  protected function getInvalidDateMessage() {
+    return pht('Repeat until date is invalid.');
+  }
+
+}
diff --git a/src/applications/phid/view/PHUIHandleListView.php b/src/applications/phid/view/PHUIHandleListView.php
--- a/src/applications/phid/view/PHUIHandleListView.php
+++ b/src/applications/phid/view/PHUIHandleListView.php
@@ -12,6 +12,7 @@
 
   private $handleList;
   private $asInline;
+  private $asText;
 
   public function setHandleList(PhabricatorHandleList $list) {
     $this->handleList = $list;
@@ -27,6 +28,15 @@
     return $this->asInline;
   }
 
+  public function setAsText($as_text) {
+    $this->asText = $as_text;
+    return $this;
+  }
+
+  public function getAsText() {
+    return $this->asText;
+  }
+
   protected function getTagName() {
     // TODO: It would be nice to render this with a proper <ul />, at least in
     // block mode, but don't stir the waters up too much for now.
@@ -37,9 +47,9 @@
     $list = $this->handleList;
     $items = array();
     foreach ($list as $handle) {
-      $view = $list->renderHandle($handle->getPHID());
-
-      $view->setShowHovercard(true);
+      $view = $list->renderHandle($handle->getPHID())
+        ->setShowHovercard(true)
+        ->setAsText($this->getAsText());
 
       $items[] = $view;
     }
diff --git a/src/applications/transactions/storage/PhabricatorModularTransactionType.php b/src/applications/transactions/storage/PhabricatorModularTransactionType.php
--- a/src/applications/transactions/storage/PhabricatorModularTransactionType.php
+++ b/src/applications/transactions/storage/PhabricatorModularTransactionType.php
@@ -86,6 +86,14 @@
     return $this->viewer;
   }
 
+  final public function getActor() {
+    return $this->getEditor()->getActor();
+  }
+
+  final public function getActingAsPHID() {
+    return $this->getEditor()->getActingAsPHID();
+  }
+
   final public function setEditor(
     PhabricatorApplicationTransactionEditor $editor) {
     $this->editor = $editor;
@@ -141,6 +149,19 @@
     return $display;
   }
 
+  final protected function renderHandleList(array $phids) {
+    $viewer = $this->getViewer();
+    $display = $viewer->renderHandleList($phids)
+      ->setAsInline(true);
+
+    $rendering_target = $this->getStorage()->getRenderingTarget();
+    if ($rendering_target == PhabricatorApplicationTransaction::TARGET_TEXT) {
+      $display->setAsText(true);
+    }
+
+    return $display;
+  }
+
   final protected function renderValue($value) {
     $rendering_target = $this->getStorage()->getRenderingTarget();
     if ($rendering_target == PhabricatorApplicationTransaction::TARGET_TEXT) {
@@ -155,6 +176,32 @@
       $value);
   }
 
+  final protected function renderOldValue() {
+    return $this->renderValue($this->getOldValue());
+  }
+
+  final protected function renderNewValue() {
+    return $this->renderValue($this->getNewValue());
+  }
+
+  final protected function renderDate($epoch) {
+    $viewer = $this->getViewer();
+
+    $display = phabricator_datetime($epoch, $viewer);
+
+    // TODO: When rendering for email, include the UTC offset. See T10633.
+
+    return $this->renderValue($display);
+  }
+
+  final protected function renderOldDate() {
+    return $this->renderDate($this->getOldValue());
+  }
+
+  final protected function renderNewDate() {
+    return $this->renderDate($this->getNewValue());
+  }
+
   final protected function newError($title, $message, $xaction = null) {
     return new PhabricatorApplicationTransactionValidationError(
       $this->getTransactionTypeConstant(),
@@ -163,4 +210,26 @@
       $xaction);
   }
 
+  final protected function newRequiredError($message, $xaction = null) {
+    return $this->newError(pht('Required'), $message, $xaction)
+      ->setIsMissingFieldError(true);
+  }
+
+  final protected function newInvalidError($message, $xaction = null) {
+    return $this->newError(pht('Invalid'), $message, $xaction);
+  }
+
+  final protected function isNewObject() {
+    return $this->getEditor()->getIsNewObject();
+  }
+
+  final protected function isEmptyTextTransaction($value, array $xactions) {
+    foreach ($xactions as $xaction) {
+      $value = $xaction->getNewValue();
+    }
+
+    return !strlen($value);
+  }
+
+
 }
diff --git a/src/infrastructure/internationalization/translation/PhabricatorUSEnglishTranslation.php b/src/infrastructure/internationalization/translation/PhabricatorUSEnglishTranslation.php
--- a/src/infrastructure/internationalization/translation/PhabricatorUSEnglishTranslation.php
+++ b/src/infrastructure/internationalization/translation/PhabricatorUSEnglishTranslation.php
@@ -1560,6 +1560,24 @@
           ),
         ),
       ),
+
+      '%s invited %s attendee(s): %s.' =>
+        '%s invited: %3$s.',
+
+      '%s uninvited %s attendee(s): %s.' =>
+        '%s uninvited: %3$s.',
+
+      '%s invited %s attendee(s): %s; uninvinted %s attendee(s): %s.' =>
+        '%s invited: %3$s; uninvited: %5$s.',
+
+      '%s invited %s attendee(s) to %s: %s.' =>
+        '%s added invites for %3$s: %4$s.',
+
+      '%s uninvited %s attendee(s) to %s: %s.' =>
+        '%s removed invites for %3$s: %4$s.',
+
+      '%s updated the invite list for %s, invited %s: %s; uninvinted %s: %s.' =>
+        '%s updated the invite list for %s, invited: %4$s; uninvited: %6$s.',
     );
   }