Index: src/__phutil_library_map__.php
===================================================================
--- src/__phutil_library_map__.php
+++ src/__phutil_library_map__.php
@@ -464,6 +464,7 @@
     'DifferentialRevisionViewController' => 'applications/differential/controller/DifferentialRevisionViewController.php',
     'DifferentialSearchIndexer' => 'applications/differential/search/DifferentialSearchIndexer.php',
     'DifferentialSubscribeController' => 'applications/differential/controller/DifferentialSubscribeController.php',
+    'DifferentialSubscribersField' => 'applications/differential/customfield/DifferentialSubscribersField.php',
     'DifferentialSummaryField' => 'applications/differential/customfield/DifferentialSummaryField.php',
     'DifferentialSummaryFieldSpecification' => 'applications/differential/field/specification/DifferentialSummaryFieldSpecification.php',
     'DifferentialTasksAttacher' => 'applications/differential/DifferentialTasksAttacher.php',
@@ -3012,6 +3013,7 @@
     'DifferentialRevisionViewController' => 'DifferentialController',
     'DifferentialSearchIndexer' => 'PhabricatorSearchDocumentIndexer',
     'DifferentialSubscribeController' => 'DifferentialController',
+    'DifferentialSubscribersField' => 'DifferentialCoreCustomField',
     'DifferentialSummaryField' => 'DifferentialCoreCustomField',
     'DifferentialSummaryFieldSpecification' => 'DifferentialFreeformFieldSpecification',
     'DifferentialTestPlanField' => 'DifferentialCoreCustomField',
Index: src/applications/differential/customfield/DifferentialCoreCustomField.php
===================================================================
--- src/applications/differential/customfield/DifferentialCoreCustomField.php
+++ src/applications/differential/customfield/DifferentialCoreCustomField.php
@@ -14,9 +14,11 @@
   abstract protected function readValueFromRevision(
     DifferentialRevision $revision);
 
-  abstract protected function writeValueToRevision(
+  protected function writeValueToRevision(
     DifferentialRevision $revision,
-    $value);
+    $value) {
+    throw new PhabricatorCustomFieldImplementationIncompleteException($this);
+  }
 
   protected function isCoreFieldRequired() {
     return false;
Index: src/applications/differential/customfield/DifferentialEditPolicyField.php
===================================================================
--- src/applications/differential/customfield/DifferentialEditPolicyField.php
+++ src/applications/differential/customfield/DifferentialEditPolicyField.php
@@ -20,12 +20,6 @@
     return $revision->getEditPolicy();
   }
 
-  protected function writeValueToRevision(
-    DifferentialRevision $revision,
-    $value) {
-    $revision->setEditPolicy($value);
-  }
-
   public function readValueFromRequest(AphrontRequest $request) {
     $this->setValue($request->getStr($this->getFieldKey()));
   }
Index: src/applications/differential/customfield/DifferentialRepositoryField.php
===================================================================
--- src/applications/differential/customfield/DifferentialRepositoryField.php
+++ src/applications/differential/customfield/DifferentialRepositoryField.php
@@ -29,7 +29,7 @@
   public function readValueFromRequest(AphrontRequest $request) {
     $phids = $request->getArr($this->getFieldKey());
     $first = head($phids);
-    $this->setValue(coalesce($first, null));
+    $this->setValue(nonempty($first, null));
   }
 
   public function getRequiredHandlePHIDsForEdit() {
@@ -41,7 +41,6 @@
   }
 
   public function renderEditControl(array $handles) {
-
     if ($this->getValue()) {
       $control_value = array_select_keys($handles, array($this->getValue()));
     } else {
@@ -97,7 +96,6 @@
         $xaction->renderHandleLink($author_phid),
         $xaction->renderHandleLink($old));
     }
-
   }
 
   public function getApplicationTransactionTitleForFeed(
Index: src/applications/differential/customfield/DifferentialSubscribersField.php
===================================================================
--- /dev/null
+++ src/applications/differential/customfield/DifferentialSubscribersField.php
@@ -0,0 +1,49 @@
+<?php
+
+final class DifferentialSubscribersField
+  extends DifferentialCoreCustomField {
+
+  public function getFieldKey() {
+    return 'differential:subscribers';
+  }
+
+  public function getFieldName() {
+    return pht('Subscribers');
+  }
+
+  public function getFieldDescription() {
+    return pht('Manage subscribers.');
+  }
+
+  protected function readValueFromRevision(
+    DifferentialRevision $revision) {
+    return PhabricatorSubscribersQuery::loadSubscribersForPHID(
+      $revision->getPHID());
+  }
+
+  public function getNewValueForApplicationTransactions() {
+    return array('=' => $this->getValue());
+  }
+
+  public function readValueFromRequest(AphrontRequest $request) {
+    $this->setValue($request->getArr($this->getFieldKey()));
+  }
+
+  public function getRequiredHandlePHIDsForEdit() {
+    return $this->getValue();
+  }
+
+  public function renderEditControl(array $handles) {
+    return id(new AphrontFormTokenizerControl())
+      ->setName($this->getFieldKey())
+      ->setDatasource('/typeahead/common/mailable/')
+      ->setValue($handles)
+      ->setError($this->getFieldError())
+      ->setLabel($this->getFieldName());
+  }
+
+  public function getApplicationTransactionType() {
+    return PhabricatorTransactions::TYPE_SUBSCRIBERS;
+  }
+
+}
Index: src/applications/differential/customfield/DifferentialViewPolicyField.php
===================================================================
--- src/applications/differential/customfield/DifferentialViewPolicyField.php
+++ src/applications/differential/customfield/DifferentialViewPolicyField.php
@@ -20,12 +20,6 @@
     return $revision->getViewPolicy();
   }
 
-  protected function writeValueToRevision(
-    DifferentialRevision $revision,
-    $value) {
-    $revision->setViewPolicy($value);
-  }
-
   public function readValueFromRequest(AphrontRequest $request) {
     $this->setValue($request->getStr($this->getFieldKey()));
   }
Index: src/applications/differential/editor/DifferentialTransactionEditor.php
===================================================================
--- src/applications/differential/editor/DifferentialTransactionEditor.php
+++ src/applications/differential/editor/DifferentialTransactionEditor.php
@@ -58,6 +58,8 @@
       case PhabricatorTransactions::TYPE_EDIT_POLICY:
         $object->setEditPolicy($xaction->getNewValue());
         return;
+      case PhabricatorTransactions::TYPE_SUBSCRIBERS:
+        return;
     }
 
     return parent::applyCustomInternalTransaction($object, $xaction);
@@ -71,6 +73,8 @@
       case PhabricatorTransactions::TYPE_VIEW_POLICY:
       case PhabricatorTransactions::TYPE_EDIT_POLICY:
         return;
+      case PhabricatorTransactions::TYPE_SUBSCRIBERS:
+        return;
     }
 
     return parent::applyCustomExternalTransaction($object, $xaction);
Index: src/applications/differential/storage/DifferentialRevision.php
===================================================================
--- src/applications/differential/storage/DifferentialRevision.php
+++ src/applications/differential/storage/DifferentialRevision.php
@@ -469,6 +469,7 @@
       new DifferentialTitleField(),
       new DifferentialSummaryField(),
       new DifferentialTestPlanField(),
+      new DifferentialSubscribersField(),
       new DifferentialRepositoryField(),
       new DifferentialViewPolicyField(),
       new DifferentialEditPolicyField(),
Index: src/applications/transactions/storage/PhabricatorApplicationTransaction.php
===================================================================
--- src/applications/transactions/storage/PhabricatorApplicationTransaction.php
+++ src/applications/transactions/storage/PhabricatorApplicationTransaction.php
@@ -186,7 +186,11 @@
   public function getHandle($phid) {
     if (empty($this->handles[$phid])) {
       throw new Exception(
-        "Transaction requires a handle ('{$phid}') it did not load.");
+        pht(
+          'Transaction ("%s") requires a handle ("%s") that it did not '.
+          'load.',
+          $this->getPHID(),
+          $phid));
     }
     return $this->handles[$phid];
   }