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
@@ -3004,6 +3004,7 @@
     'PhabricatorSearchEditController' => 'applications/search/controller/PhabricatorSearchEditController.php',
     'PhabricatorSearchEngine' => 'applications/search/engine/PhabricatorSearchEngine.php',
     'PhabricatorSearchEngineAPIMethod' => 'applications/search/engine/PhabricatorSearchEngineAPIMethod.php',
+    'PhabricatorSearchEngineAttachment' => 'applications/search/engineextension/PhabricatorSearchEngineAttachment.php',
     'PhabricatorSearchEngineExtension' => 'applications/search/engineextension/PhabricatorSearchEngineExtension.php',
     'PhabricatorSearchEngineExtensionModule' => 'applications/search/engineextension/PhabricatorSearchEngineExtensionModule.php',
     'PhabricatorSearchEngineTestCase' => 'applications/search/engine/__tests__/PhabricatorSearchEngineTestCase.php',
@@ -3149,6 +3150,7 @@
     'PhabricatorSubscriptionsListController' => 'applications/subscriptions/controller/PhabricatorSubscriptionsListController.php',
     'PhabricatorSubscriptionsRemoveSelfHeraldAction' => 'applications/subscriptions/herald/PhabricatorSubscriptionsRemoveSelfHeraldAction.php',
     'PhabricatorSubscriptionsRemoveSubscribersHeraldAction' => 'applications/subscriptions/herald/PhabricatorSubscriptionsRemoveSubscribersHeraldAction.php',
+    'PhabricatorSubscriptionsSearchEngineAttachment' => 'applications/subscriptions/engineextension/PhabricatorSubscriptionsSearchEngineAttachment.php',
     'PhabricatorSubscriptionsSearchEngineExtension' => 'applications/subscriptions/engineextension/PhabricatorSubscriptionsSearchEngineExtension.php',
     'PhabricatorSubscriptionsSubscribeEmailCommand' => 'applications/subscriptions/command/PhabricatorSubscriptionsSubscribeEmailCommand.php',
     'PhabricatorSubscriptionsSubscribersPolicyRule' => 'applications/subscriptions/policyrule/PhabricatorSubscriptionsSubscribersPolicyRule.php',
@@ -7321,6 +7323,7 @@
     'PhabricatorSearchEditController' => 'PhabricatorSearchBaseController',
     'PhabricatorSearchEngine' => 'Phobject',
     'PhabricatorSearchEngineAPIMethod' => 'ConduitAPIMethod',
+    'PhabricatorSearchEngineAttachment' => 'Phobject',
     'PhabricatorSearchEngineExtension' => 'Phobject',
     'PhabricatorSearchEngineExtensionModule' => 'PhabricatorConfigModule',
     'PhabricatorSearchEngineTestCase' => 'PhabricatorTestCase',
@@ -7482,6 +7485,7 @@
     'PhabricatorSubscriptionsListController' => 'PhabricatorController',
     'PhabricatorSubscriptionsRemoveSelfHeraldAction' => 'PhabricatorSubscriptionsHeraldAction',
     'PhabricatorSubscriptionsRemoveSubscribersHeraldAction' => 'PhabricatorSubscriptionsHeraldAction',
+    'PhabricatorSubscriptionsSearchEngineAttachment' => 'PhabricatorSearchEngineAttachment',
     'PhabricatorSubscriptionsSearchEngineExtension' => 'PhabricatorSearchEngineExtension',
     'PhabricatorSubscriptionsSubscribeEmailCommand' => 'MetaMTAEmailTransactionCommand',
     'PhabricatorSubscriptionsSubscribersPolicyRule' => 'PhabricatorPolicyRule',
diff --git a/src/applications/search/engine/PhabricatorApplicationSearchEngine.php b/src/applications/search/engine/PhabricatorApplicationSearchEngine.php
--- a/src/applications/search/engine/PhabricatorApplicationSearchEngine.php
+++ b/src/applications/search/engine/PhabricatorApplicationSearchEngine.php
@@ -1123,10 +1123,25 @@
 
     $this->saveQuery($saved_query);
 
-
     $query = $this->buildQueryFromSavedQuery($saved_query);
     $pager = $this->newPagerForSavedQuery($saved_query);
 
+    $attachments = $this->getConduitSearchAttachments();
+
+    // TODO: Validate this better.
+    $attachment_specs = $request->getValue('attachments');
+    $attachments = array_select_keys(
+      $attachments,
+      array_keys($attachment_specs));
+
+    foreach ($attachments as $key => $attachment) {
+      $attachment->setViewer($viewer);
+    }
+
+    foreach ($attachments as $key => $attachment) {
+      $attachment->willLoadAttachmentData($query, $attachment_specs[$key]);
+    }
+
     $this->setQueryOrderForConduit($query, $request);
     $this->setPagerLimitForConduit($pager, $request);
     $this->setPagerOffsetsForConduit($pager, $request);
@@ -1137,10 +1152,36 @@
     if ($objects) {
       $field_extensions = $this->getConduitFieldExtensions();
 
+      $attachment_data = array();
+      foreach ($attachments as $key => $attachment) {
+        $attachment_data[$key] = $attachment->loadAttachmentData(
+          $objects,
+          $attachment_specs[$key]);
+      }
+
       foreach ($objects as $object) {
-        $data[] = $this->getObjectWireFormatForConduit(
+        $field_map = $this->getObjectWireFieldsForConduit(
           $object,
           $field_extensions);
+
+        $attachment_map = array();
+        foreach ($attachments as $key => $attachment) {
+          $attachment_map[$key] = $attachment->getAttachmentForObject(
+            $object,
+            $attachment_data[$key],
+            $attachment_specs[$key]);
+        }
+
+        $id = (int)$object->getID();
+        $phid = $object->getPHID();
+
+        $data[] = array(
+          'id' => $id,
+          'type' => phid_get_type($phid),
+          'phid' => $phid,
+          'fields' => $field_map,
+          'attachments' => $attachment_map,
+        );
       }
     }
 
@@ -1264,21 +1305,6 @@
     }
   }
 
-  protected function getObjectWireFormatForConduit(
-    $object,
-    array $field_extensions) {
-    $phid = $object->getPHID();
-
-    return array(
-      'id' => (int)$object->getID(),
-      'type' => phid_get_type($phid),
-      'phid' => $phid,
-      'fields' => $this->getObjectWireFieldsForConduit(
-        $object,
-        $field_extensions),
-    );
-  }
-
   protected function getObjectWireFieldsForConduit(
     $object,
     array $field_extensions) {
@@ -1291,4 +1317,29 @@
     return $fields;
   }
 
+  public function getConduitSearchAttachments() {
+    $extensions = $this->getEngineExtensions();
+
+    $attachments = array();
+    foreach ($extensions as $extension) {
+      $extension_attachments = $extension->getSearchAttachments();
+      foreach ($extension_attachments as $attachment) {
+        $attachment_key = $attachment->getAttachmentKey();
+        if (isset($attachments[$attachment_key])) {
+          $other = $attachments[$attachment_key];
+          throw new Exception(
+            pht(
+              'Two search engine attachments (of classes "%s" and "%s") '.
+              'specify the same attachment key ("%s"); keys must be unique.',
+              get_class($attachment),
+              get_class($other),
+              $attachment_key));
+        }
+        $attachments[$attachment_key] = $attachment;
+      }
+    }
+
+    return $attachments;
+  }
+
 }
diff --git a/src/applications/search/engine/PhabricatorSearchEngineAPIMethod.php b/src/applications/search/engine/PhabricatorSearchEngineAPIMethod.php
--- a/src/applications/search/engine/PhabricatorSearchEngineAPIMethod.php
+++ b/src/applications/search/engine/PhabricatorSearchEngineAPIMethod.php
@@ -23,6 +23,7 @@
     return array(
       'queryKey' => 'optional string',
       'constraints' => 'optional map<string, wild>',
+      'attachments' => 'optional map<string, bool>',
       'order' => 'optional order',
     ) + $this->getPagerParamTypes();
   }
@@ -58,6 +59,7 @@
     $out[] = $this->buildConstraintsBox($engine);
     $out[] = $this->buildOrderBox($engine, $query);
     $out[] = $this->buildFieldsBox($engine);
+    $out[] = $this->buildAttachmentsBox($engine);
     $out[] = $this->buildPagingBox($engine);
 
     return $out;
@@ -401,6 +403,94 @@
       ->appendChild($table);
   }
 
+  private function buildAttachmentsBox(
+    PhabricatorApplicationSearchEngine $engine) {
+
+    $info = pht(<<<EOTEXT
+By default, only basic information about objects is returned. If you want
+more extensive information, you can use available `attachments` to get more
+information in the results (like subscribers and projects).
+
+Generally, requesting more information means the query executes more slowly
+and returns more data (in some cases, much more data). You should normally
+request only the data you need.
+
+To request extra data, specify which attachments you want in the `attachments`
+parameter:
+
+```lang=json, name="Example Attachments Request"
+{
+  ...
+  "attachments": {
+    "subscribers": true
+  },
+  ...
+}
+```
+
+This example specifies that results should include information about
+subscribers. In the return value, each object will now have this information
+filled out in the corresponding `attachments` value:
+
+```lang=json, name="Example Attachments Result"
+{
+  ...
+  "data": [
+    {
+      ...
+      "attachments": {
+        "subscribers": {
+          "subscriberPHIDs": [
+            "PHID-WXYZ-2222",
+          ],
+          "subscriberCount": 1,
+          "viewerIsSubscribed": false
+        }
+      },
+      ...
+    },
+    ...
+  ],
+  ...
+}
+```
+
+These attachments are available:
+EOTEXT
+      );
+
+    $attachments = $engine->getConduitSearchAttachments();
+
+    $rows = array();
+    foreach ($attachments as $key => $attachment) {
+      $rows[] = array(
+        $key,
+        $attachment->getAttachmentName(),
+        $attachment->getAttachmentDescription(),
+      );
+    }
+
+    $table = id(new AphrontTableView($rows))
+      ->setHeaders(
+        array(
+          pht('Key'),
+          pht('Name'),
+          pht('Description'),
+        ))
+      ->setColumnClasses(
+        array(
+          'prewrap',
+          'pri',
+          'wide',
+        ));
+
+    return id(new PHUIObjectBoxView())
+      ->setHeaderText(pht('Attachments'))
+      ->setCollapsed(true)
+      ->appendChild($this->buildRemarkup($info))
+      ->appendChild($table);
+  }
+
   private function buildPagingBox(
     PhabricatorApplicationSearchEngine $engine) {
 
diff --git a/src/applications/search/engineextension/PhabricatorSearchEngineAttachment.php b/src/applications/search/engineextension/PhabricatorSearchEngineAttachment.php
new file mode 100644
--- /dev/null
+++ b/src/applications/search/engineextension/PhabricatorSearchEngineAttachment.php
@@ -0,0 +1,50 @@
+<?php
+
+abstract class PhabricatorSearchEngineAttachment extends Phobject {
+
+  private $attachmentKey;
+  private $viewer;
+  private $searchEngine;
+
+  final public function setViewer($viewer) {
+    $this->viewer = $viewer;
+    return $this;
+  }
+
+  final public function getViewer() {
+    return $this->viewer;
+  }
+
+  final public function setSearchEngine(
+    PhabricatorApplicationSearchEngine $engine) {
+    $this->searchEngine = $engine;
+    return $this;
+  }
+
+  final public function getSearchEngine() {
+    return $this->searchEngine;
+  }
+
+  public function setAttachmentKey($attachment_key) {
+    $this->attachmentKey = $attachment_key;
+    return $this;
+  }
+
+  public function getAttachmentKey() {
+    return $this->attachmentKey;
+  }
+
+  abstract public function getAttachmentName();
+  abstract public function getAttachmentDescription();
+
+  public function willLoadAttachmentData($query, $spec) {
+    return;
+  }
+
+  public function loadAttachmentData(array $objects, $spec) {
+    return null;
+  }
+
+  abstract public function getAttachmentForObject($object, $data, $spec);
+
+}
diff --git a/src/applications/search/engineextension/PhabricatorSearchEngineExtension.php b/src/applications/search/engineextension/PhabricatorSearchEngineExtension.php
--- a/src/applications/search/engineextension/PhabricatorSearchEngineExtension.php
+++ b/src/applications/search/engineextension/PhabricatorSearchEngineExtension.php
@@ -40,6 +40,10 @@
     return array();
   }
 
+  public function getSearchAttachments() {
+    return array();
+  }
+
   public function applyConstraintsToQuery(
     $object,
     $query,
diff --git a/src/applications/subscriptions/engineextension/PhabricatorSubscriptionsSearchEngineAttachment.php b/src/applications/subscriptions/engineextension/PhabricatorSubscriptionsSearchEngineAttachment.php
new file mode 100644
--- /dev/null
+++ b/src/applications/subscriptions/engineextension/PhabricatorSubscriptionsSearchEngineAttachment.php
@@ -0,0 +1,84 @@
+<?php
+
+final class PhabricatorSubscriptionsSearchEngineAttachment
+  extends PhabricatorSearchEngineAttachment {
+
+  public function getAttachmentName() {
+    return pht('Subscribers');
+  }
+
+  public function getAttachmentDescription() {
+    return pht('Get information about subscribers.');
+  }
+
+  public function loadAttachmentData(array $objects, $spec) {
+    $object_phids = mpull($objects, 'getPHID');
+    $edge_type = PhabricatorObjectHasSubscriberEdgeType::EDGECONST;
+
+
+    $subscribers_query = id(new PhabricatorEdgeQuery())
+      ->withSourcePHIDs($object_phids)
+      ->withEdgeTypes(array($edge_type));
+    $subscribers_query->execute();
+
+    $viewer = $this->getViewer();
+    $viewer_phid = $viewer->getPHID();
+    if ($viewer) {
+      $edges = id(new PhabricatorEdgeQuery())
+        ->withSourcePHIDs($object_phids)
+        ->withEdgeTypes(array($edge_type))
+        ->withDestinationPHIDs(array($viewer_phid))
+        ->execute();
+
+      $viewer_map = array();
+      foreach ($edges as $object_phid => $types) {
+        if ($types[$edge_type]) {
+          $viewer_map[$object_phid] = true;
+        }
+      }
+    } else {
+      $viewer_map = array();
+    }
+
+    return array(
+      'subscribers.query' => $subscribers_query,
+      'viewer.map' => $viewer_map,
+    );
+  }
+
+  public function getAttachmentForObject($object, $data, $spec) {
+    $subscribers_query = idx($data, 'subscribers.query');
+    $viewer_map = idx($data, 'viewer.map');
+    $object_phid = $object->getPHID();
+
+    $subscribed_phids = $subscribers_query->getDestinationPHIDs(
+      array($object_phid),
+      array(PhabricatorObjectHasSubscriberEdgeType::EDGECONST));
+    $subscribed_count = count($subscribed_phids);
+    if ($subscribed_count > 10) {
+      $subscribed_phids = array_slice($subscribed_phids, 0, 10);
+    }
+
+    $subscribed_phids = array_values($subscribed_phids);
+
+    $viewer = $this->getViewer();
+    $viewer_phid = $viewer->getPHID();
+
+    if (!$viewer_phid) {
+      $self_subscribed = false;
+    } else if (isset($viewer_map[$object_phid])) {
+      $self_subscribed = true;
+    } else if ($object->isAutomaticallySubscribed($viewer_phid)) {
+      $self_subscribed = true;
+    } else {
+      $self_subscribed = false;
+    }
+
+    return array(
+      'subscriberPHIDs' => $subscribed_phids,
+      'subscriberCount' => $subscribed_count,
+      'viewerIsSubscribed' => $self_subscribed,
+    );
+  }
+
+}
diff --git a/src/applications/subscriptions/engineextension/PhabricatorSubscriptionsSearchEngineExtension.php b/src/applications/subscriptions/engineextension/PhabricatorSubscriptionsSearchEngineExtension.php
--- a/src/applications/subscriptions/engineextension/PhabricatorSubscriptionsSearchEngineExtension.php
+++ b/src/applications/subscriptions/engineextension/PhabricatorSubscriptionsSearchEngineExtension.php
@@ -50,5 +50,11 @@
     return $fields;
   }
 
+  public function getSearchAttachments() {
+    return array(
+      id(new PhabricatorSubscriptionsSearchEngineAttachment())
+        ->setAttachmentKey('subscribers'),
+    );
+  }
 
 }
diff --git a/src/applications/transactions/editfield/PhabricatorEditField.php b/src/applications/transactions/editfield/PhabricatorEditField.php
--- a/src/applications/transactions/editfield/PhabricatorEditField.php
+++ b/src/applications/transactions/editfield/PhabricatorEditField.php
@@ -516,7 +516,7 @@
     $edit_type = $this->getEditType();
 
     if ($edit_type === null) {
-      return null;
+      return array();
     }
 
     return array($edit_type);
@@ -526,7 +526,7 @@
     $edit_type = $this->getEditType();
 
     if ($edit_type === null) {
-      return null;
+      return array();
     }
 
     return array($edit_type);