diff --git a/resources/celerity/map.php b/resources/celerity/map.php
--- a/resources/celerity/map.php
+++ b/resources/celerity/map.php
@@ -7,8 +7,8 @@
  */
 return array(
   'names' => array(
-    'core.pkg.css' => 'a2a90172',
-    'core.pkg.js' => 'd57952b0',
+    'core.pkg.css' => 'f7d01efc',
+    'core.pkg.js' => 'a1f9db42',
     'darkconsole.pkg.js' => '8ab24e01',
     'differential.pkg.css' => '3500921f',
     'differential.pkg.js' => 'c0506961',
@@ -34,7 +34,7 @@
     'rsrc/css/aphront/typeahead.css' => '0e403212',
     'rsrc/css/application/almanac/almanac.css' => 'dbb9b3af',
     'rsrc/css/application/auth/auth.css' => '1e655982',
-    'rsrc/css/application/base/main-menu-view.css' => 'c648b2f5',
+    'rsrc/css/application/base/main-menu-view.css' => '31e66da9',
     'rsrc/css/application/base/notification-menu.css' => '3c9d8aa1',
     'rsrc/css/application/base/phabricator-application-launch-view.css' => '16ca323f',
     'rsrc/css/application/base/standard-page-view.css' => 'd3e1abe9',
@@ -486,7 +486,7 @@
     'rsrc/js/core/behavior-reorder-applications.js' => '76b9fc3e',
     'rsrc/js/core/behavior-reveal-content.js' => '60821bc7',
     'rsrc/js/core/behavior-scrollbar.js' => '834a1173',
-    'rsrc/js/core/behavior-search-typeahead.js' => '724b1247',
+    'rsrc/js/core/behavior-search-typeahead.js' => 'bc965352',
     'rsrc/js/core/behavior-select-on-click.js' => '4e3e79a6',
     'rsrc/js/core/behavior-toggle-class.js' => 'e566f52c',
     'rsrc/js/core/behavior-tokenizer.js' => 'b3a4b884',
@@ -628,7 +628,7 @@
     'javelin-behavior-phabricator-oncopy' => '2926fff2',
     'javelin-behavior-phabricator-remarkup-assist' => 'e32d14ab',
     'javelin-behavior-phabricator-reveal-content' => '60821bc7',
-    'javelin-behavior-phabricator-search-typeahead' => '724b1247',
+    'javelin-behavior-phabricator-search-typeahead' => 'bc965352',
     'javelin-behavior-phabricator-show-older-transactions' => 'dbbf48b6',
     'javelin-behavior-phabricator-tooltips' => '3ee3408b',
     'javelin-behavior-phabricator-transaction-comment-form' => '9f7309fb',
@@ -737,7 +737,7 @@
     'phabricator-hovercard-view-css' => '44394670',
     'phabricator-keyboard-shortcut' => '1ae869f2',
     'phabricator-keyboard-shortcut-manager' => 'c1700f6f',
-    'phabricator-main-menu-view' => 'c648b2f5',
+    'phabricator-main-menu-view' => '31e66da9',
     'phabricator-nav-view-css' => '7aeaf435',
     'phabricator-notification' => '0c6946e7',
     'phabricator-notification-css' => '9c279160',
@@ -1367,16 +1367,6 @@
       'javelin-vector',
       'javelin-util',
     ),
-    '724b1247' => array(
-      'javelin-behavior',
-      'javelin-typeahead-ondemand-source',
-      'javelin-typeahead',
-      'javelin-dom',
-      'javelin-uri',
-      'javelin-util',
-      'javelin-stratcom',
-      'phabricator-prefab',
-    ),
     '7319e029' => array(
       'javelin-behavior',
       'javelin-dom',
@@ -1749,6 +1739,16 @@
       'javelin-mask',
       'phabricator-drag-and-drop-file-upload',
     ),
+    'bc965352' => array(
+      'javelin-behavior',
+      'javelin-typeahead-ondemand-source',
+      'javelin-typeahead',
+      'javelin-dom',
+      'javelin-uri',
+      'javelin-util',
+      'javelin-stratcom',
+      'phabricator-prefab',
+    ),
     'bd4c8dca' => array(
       'javelin-install',
       'javelin-util',
diff --git a/src/applications/base/PhabricatorApplication.php b/src/applications/base/PhabricatorApplication.php
--- a/src/applications/base/PhabricatorApplication.php
+++ b/src/applications/base/PhabricatorApplication.php
@@ -582,4 +582,8 @@
     }
   }
 
+  public function getApplicationSearchDocumentTypes() {
+    return array();
+  }
+
 }
diff --git a/src/applications/maniphest/application/PhabricatorManiphestApplication.php b/src/applications/maniphest/application/PhabricatorManiphestApplication.php
--- a/src/applications/maniphest/application/PhabricatorManiphestApplication.php
+++ b/src/applications/maniphest/application/PhabricatorManiphestApplication.php
@@ -158,4 +158,10 @@
     );
   }
 
+  public function getApplicationSearchDocumentTypes() {
+    return array(
+      ManiphestTaskPHIDType::TYPECONST,
+    );
+  }
+
 }
diff --git a/src/applications/search/controller/PhabricatorApplicationSearchController.php b/src/applications/search/controller/PhabricatorApplicationSearchController.php
--- a/src/applications/search/controller/PhabricatorApplicationSearchController.php
+++ b/src/applications/search/controller/PhabricatorApplicationSearchController.php
@@ -233,6 +233,15 @@
             $saved_query);
         }
 
+        $messages = $engine->getMessages();
+        if ($messages) {
+          $nav->appendChild(
+            id(new PHUIInfoView())
+              ->setSeverity(PHUIInfoView::SEVERITY_NOTICE)
+              ->setErrors($messages));
+        }
+
+
         $nav->appendChild($list);
 
         // TODO: This is a bit hacky.
diff --git a/src/applications/search/controller/PhabricatorSearchController.php b/src/applications/search/controller/PhabricatorSearchController.php
--- a/src/applications/search/controller/PhabricatorSearchController.php
+++ b/src/applications/search/controller/PhabricatorSearchController.php
@@ -3,6 +3,8 @@
 final class PhabricatorSearchController
   extends PhabricatorSearchBaseController {
 
+  const SCOPE_CURRENT_APPLICATION = 'application';
+
   private $queryKey;
 
   public function shouldAllowPublic() {
@@ -32,49 +34,69 @@
     $engine = new PhabricatorSearchApplicationSearchEngine();
     $engine->setViewer($viewer);
 
-    // NOTE: This is a little weird. If we're coming from primary search, we
-    // load the user's first search filter and overwrite the "query" part of
-    // it, then send them to that result page. This is sort of odd, but lets
-    // users choose a default query like "Open Tasks" in a reasonable way,
-    // with only this piece of somewhat-sketchy code. See discussion in T4365.
-
+    // If we're coming from primary search, do some special handling to
+    // interpret the scope selector and query.
     if ($request->getBool('search:primary')) {
+
+      // If there's no query, just take the user to advanced search.
       if (!strlen($request->getStr('query'))) {
         $advanced_uri = '/search/query/advanced/';
         return id(new AphrontRedirectResponse())->setURI($advanced_uri);
       }
 
-      $named_queries = $engine->loadEnabledNamedQueries();
-      if ($named_queries) {
-        $named = head($named_queries);
-
-        $query_key = $named->getQueryKey();
-        $saved = null;
-        if ($engine->isBuiltinQuery($query_key)) {
-          $saved = $engine->buildSavedQueryFromBuiltin($query_key);
-        } else {
-          $saved = id(new PhabricatorSavedQueryQuery())
-            ->setViewer($viewer)
-            ->withQueryKeys(array($query_key))
-            ->executeOne();
+      // First, load or construct a template for the search by examining
+      // the current search scope.
+      $scope = $request->getStr('search:scope');
+      $saved = null;
+
+      $app_scope_error = false;
+      if ($scope == self::SCOPE_CURRENT_APPLICATION) {
+        $app_scope_error = true;
+        $application = id(new PhabricatorApplicationQuery())
+          ->setViewer($viewer)
+          ->withClasses(array($request->getStr('search:application')))
+          ->executeOne();
+        if ($application) {
+          $types = $application->getApplicationSearchDocumentTypes();
+          if ($types) {
+            $app_scope_error = false;
+            $saved = id(new PhabricatorSavedQuery())
+              ->setEngineClassName(get_class($engine))
+              ->setParameter('types', $types);
+          }
         }
+      }
 
-        if ($saved) {
-          $saved->setParameter('query', $request->getStr('query'));
-          $unguarded = AphrontWriteGuard::beginScopedUnguardedWrites();
-            try {
-              $saved->setID(null)->save();
-            } catch (AphrontDuplicateKeyQueryException $ex) {
-              // Ignore, this is just a repeated search.
-            }
-          unset($unguarded);
-
-          $results_uri = $engine->getQueryResultsPageURI(
-            $saved->getQueryKey()).'#R';
+      if (!$saved && !$engine->isBuiltinQuery($scope)) {
+        $saved = id(new PhabricatorSavedQueryQuery())
+          ->setViewer($viewer)
+          ->withQueryKeys(array($scope))
+          ->executeOne();
+      }
 
-          return id(new AphrontRedirectResponse())->setURI($results_uri);
+      if (!$saved) {
+        if (!$engine->isBuiltinQuery($scope)) {
+          $scope = 'all';
         }
+        $saved = $engine->buildSavedQueryFromBuiltin($scope);
       }
+
+      // Add the user's query, then save this as a new saved query and send
+      // the user to the results page.
+      $saved->setParameter('query', $request->getStr('query'));
+      $saved->setParameter('app.scope.error', $app_scope_error);
+
+      $unguarded = AphrontWriteGuard::beginScopedUnguardedWrites();
+        try {
+          $saved->setID(null)->save();
+        } catch (AphrontDuplicateKeyQueryException $ex) {
+          // Ignore, this is just a repeated search.
+        }
+      unset($unguarded);
+
+      $query_key = $saved->getQueryKey();
+      $results_uri = $engine->getQueryResultsPageURI($query_key).'#R';
+      return id(new AphrontRedirectResponse())->setURI($results_uri);
     }
 
     $controller = id(new PhabricatorApplicationSearchController())
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
@@ -19,6 +19,7 @@
   private $application;
   private $viewer;
   private $errors = array();
+  private $messages = array();
   private $customFields = false;
   private $request;
   private $context;
@@ -101,6 +102,15 @@
     return $this;
   }
 
+  public function getMessages() {
+    return $this->messages;
+  }
+
+  public function addMessage($message) {
+    $this->messages[] = $message;
+    return $this;
+  }
+
   /**
    * Return an application URI corresponding to the results page of a query.
    * Normally, this is something like `/application/query/QUERYKEY/`.
diff --git a/src/applications/search/query/PhabricatorSearchApplicationSearchEngine.php b/src/applications/search/query/PhabricatorSearchApplicationSearchEngine.php
--- a/src/applications/search/query/PhabricatorSearchApplicationSearchEngine.php
+++ b/src/applications/search/query/PhabricatorSearchApplicationSearchEngine.php
@@ -55,6 +55,14 @@
     AphrontFormView $form,
     PhabricatorSavedQuery $saved) {
 
+    if ($saved->getParameter('app.scope.error')) {
+      $this->addMessage(
+        pht(
+          'You ran a "Current Application" search, but the current '.
+          'application does not have any searchable document types. '.
+          'Showing results for all documents.'));
+    }
+
     $options = array();
     $author_value = null;
     $owner_value = null;
diff --git a/src/applications/settings/storage/PhabricatorUserPreferences.php b/src/applications/settings/storage/PhabricatorUserPreferences.php
--- a/src/applications/settings/storage/PhabricatorUserPreferences.php
+++ b/src/applications/settings/storage/PhabricatorUserPreferences.php
@@ -19,6 +19,7 @@
 
   const PREFERENCE_SEARCHBAR_JUMP       = 'searchbar-jump';
   const PREFERENCE_SEARCH_SHORTCUT      = 'search-shortcut';
+  const PREFERENCE_SEARCH_SCOPE = 'search-scope';
 
   const PREFERENCE_DIFFUSION_BLAME      = 'diffusion-blame';
   const PREFERENCE_DIFFUSION_COLOR      = 'diffusion-color';
diff --git a/src/view/page/menu/PhabricatorMainMenuSearchView.php b/src/view/page/menu/PhabricatorMainMenuSearchView.php
--- a/src/view/page/menu/PhabricatorMainMenuSearchView.php
+++ b/src/view/page/menu/PhabricatorMainMenuSearchView.php
@@ -3,6 +3,16 @@
 final class PhabricatorMainMenuSearchView extends AphrontView {
 
   private $id;
+  private $application;
+
+  public function setApplication(PhabricatorApplication $application) {
+    $this->application = $application;
+    return $this;
+  }
+
+  public function getApplication() {
+    return $this->application;
+  }
 
   public function getID() {
     if (!$this->id) {
@@ -36,6 +46,7 @@
       '');
 
     $search_datasource = new PhabricatorSearchDatasource();
+    $scope_key = PhabricatorUserPreferences::PREFERENCE_SEARCH_SCOPE;
 
     Javelin::initBehavior(
       'phabricator-search-typeahead',
@@ -46,6 +57,7 @@
         'src'         => $search_datasource->getDatasourceURI(),
         'limit'       => 10,
         'placeholder' => pht('Search'),
+        'scopeUpdateURI' => '/settings/adjust/?key='.$scope_key,
       ));
 
     $primary_input = phutil_tag(
@@ -63,6 +75,8 @@
       ),
       pht('Search'));
 
+    $selector = $this->buildModeSelector();
+
     $form = phabricator_form(
       $user,
       array(
@@ -78,6 +92,7 @@
             'class' => 'phui-icon-view phui-font-fa fa-search',
             ),
           $search_text),
+        $selector,
         $primary_input,
         $target,
       )));
@@ -85,4 +100,124 @@
     return $form;
   }
 
+  private function buildModeSelector() {
+    $viewer = $this->getUser();
+
+    $items = array();
+    $items[] = array(
+      'name' => pht('Search'),
+    );
+
+    $items[] = array(
+      'icon' => 'fa-globe',
+      'name' => pht('Search All Documents'),
+      'value' => 'all',
+    );
+
+    $application_value = null;
+    $application_icon = 'fa-file-o';
+    $application = $this->getApplication();
+    if ($application) {
+      $application_value = get_class($application);
+      if ($application->getApplicationSearchDocumentTypes()) {
+        $application_icon = $application->getFontIcon();
+      }
+    }
+
+    $items[] = array(
+      'icon' => $application_icon,
+      'name' => pht('Search Current Application'),
+      'value' => PhabricatorSearchController::SCOPE_CURRENT_APPLICATION,
+    );
+
+    $items[] = array(
+      'name' => pht('Saved Queries'),
+    );
+
+
+    $engine = id(new PhabricatorSearchApplicationSearchEngine())
+      ->setViewer($viewer);
+    $engine_queries = $engine->loadEnabledNamedQueries();
+    $query_map = mpull($engine_queries, 'getQueryName', 'getQueryKey');
+    foreach ($query_map as $query_key => $query_name) {
+      if ($query_key == 'all') {
+        // Skip the builtin "All" query since it's redundant with the default
+        // setting.
+        continue;
+      }
+
+      $items[] = array(
+        'icon' => 'fa-search',
+        'name' => $query_name,
+        'value' => $query_key,
+      );
+    }
+
+    $items[] =  array(
+      'name' => pht('More Options'),
+    );
+
+    $items[] = array(
+      'icon' => 'fa-search-plus',
+      'name' => pht('Advanced Search'),
+      'href' => '/search/query/advanced/',
+    );
+
+    /* TODO: Write this.
+    $items[] = array(
+      'icon' => 'fa-book',
+      'name' => pht('User Guide: Search'),
+      'href' => PhabricatorEnv::getDoclink('User Guide: Search'),
+    );
+    */
+
+    $scope_key = PhabricatorUserPreferences::PREFERENCE_SEARCH_SCOPE;
+    $current_value = $viewer->loadPreferences()->getPreference(
+      $scope_key,
+      'all');
+
+    $current_icon = 'fa-globe';
+    foreach ($items as $item) {
+      if (idx($item, 'value') == $current_value) {
+        $current_icon = $item['icon'];
+        break;
+      }
+    }
+
+    $selector = id(new PHUIButtonView())
+      ->addClass('phabricator-main-menu-search-dropdown')
+      ->addSigil('global-search-dropdown')
+      ->setMetadata(
+        array(
+          'items' => $items,
+          'icon' => $current_icon,
+          'value' => $current_value,
+        ))
+      ->setIcon(
+        id(new PHUIIconView())
+          ->addSigil('global-search-dropdown-icon')
+          ->setIconFont($current_icon))
+      ->setDropdown(true);
+
+    $input = javelin_tag(
+      'input',
+      array(
+        'type' => 'hidden',
+        'sigil' => 'global-search-dropdown-input',
+        'name' => 'search:scope',
+        'value' => $current_value,
+      ));
+
+    $application_input = javelin_tag(
+      'input',
+      array(
+        'type' => 'hidden',
+        'sigil' => 'global-search-dropdown-app',
+        'name' => 'search:application',
+        'value' => $application_value,
+      ));
+
+    return array($selector, $input, $application_input);
+  }
+
 }
diff --git a/src/view/page/menu/PhabricatorMainMenuView.php b/src/view/page/menu/PhabricatorMainMenuView.php
--- a/src/view/page/menu/PhabricatorMainMenuView.php
+++ b/src/view/page/menu/PhabricatorMainMenuView.php
@@ -114,6 +114,16 @@
     if ($show_search) {
       $search = new PhabricatorMainMenuSearchView();
       $search->setUser($user);
+
+      $application = null;
+      $controller = $this->getController();
+      if ($controller) {
+        $application = $controller->getCurrentApplication();
+      }
+      if ($application) {
+        $search->setApplication($application);
+      }
+
       $result = $search;
 
       $pref_shortcut = PhabricatorUserPreferences::PREFERENCE_SEARCH_SHORTCUT;
diff --git a/webroot/rsrc/css/application/base/main-menu-view.css b/webroot/rsrc/css/application/base/main-menu-view.css
--- a/webroot/rsrc/css/application/base/main-menu-view.css
+++ b/webroot/rsrc/css/application/base/main-menu-view.css
@@ -160,10 +160,9 @@
   height: 28px;
   line-height: 12px;
   box-shadow: 0px 1px 1px rgba(128, 128, 128, 0.25);
-  padding: 6px 30px 6px 6px;
+  padding: 6px 30px 6px 46px;
   float: left;
   width: 205px;
-  left: 0;
 }
 
 .phabricator-main-menu.main-header-dark .phabricator-main-menu-search input {
@@ -207,6 +206,25 @@
   border-radius: 0;
 }
 
+.phabricator-main-menu-search button.phabricator-main-menu-search-dropdown {
+  position: absolute;
+  right: auto;
+  left: 0;
+  width: 40px;
+}
+
+.phabricator-main-menu-search button.phabricator-main-menu-search-dropdown
+  .phui-icon-view {
+  color: rgba(255,255,255,.8);
+}
+
+.phabricator-main-menu-search-dropdown .caret {
+  position: absolute;
+  right: 4px;
+  top: 3px;
+}
+
+
 .phabricator-main-menu-search button:hover {
   color: #fff;
 }
diff --git a/webroot/rsrc/js/core/behavior-search-typeahead.js b/webroot/rsrc/js/core/behavior-search-typeahead.js
--- a/webroot/rsrc/js/core/behavior-search-typeahead.js
+++ b/webroot/rsrc/js/core/behavior-search-typeahead.js
@@ -143,4 +143,86 @@
     typeahead.setPlaceholder('');
     typeahead.updatePlaceHolder();
   });
+
+  // TODO: Quicksand needs to update the application search input as we change
+  // applications; we should register a listener.
+  // TODO: Quicksand also needs to update the application search icon on the
+  // button itself and in the menu.
+
+  // Implement the scope selector menu for the global search.
+  JX.Stratcom.listen('click', 'global-search-dropdown', function(e) {
+    var data = e.getNodeData('global-search-dropdown');
+    var button = e.getNode('global-search-dropdown');
+    if (data.menu) {
+      return;
+    }
+
+    e.kill();
+
+    function updateValue(spec) {
+      if (data.value == spec.value) {
+        return;
+      }
+
+      // Swap out the icon.
+      var icon = JX.DOM.find(button, 'span', 'global-search-dropdown-icon');
+      JX.DOM.alterClass(icon, data.icon, false);
+      data.icon = spec.icon;
+      JX.DOM.alterClass(icon, data.icon, true);
+
+      // Update the value.
+      data.value = spec.value;
+
+      // Update the form input.
+      var frame = button.parentNode;
+      var input = JX.DOM.find(frame, 'input', 'global-search-dropdown-input');
+      input.value = data.value;
+
+      new JX.Request(config.scopeUpdateURI)
+        .setData({value: data.value})
+        .send();
+    }
+
+    var menu = new JX.PHUIXDropdownMenu(button)
+      .setAlign('left');
+    data.menu = menu;
+
+    menu.listen('open', function() {
+      var list = new JX.PHUIXActionListView();
+
+      for (var ii = 0; ii < data.items.length; ii++) {
+        var spec = data.items[ii];
+        var item = new JX.PHUIXActionView()
+          .setName(spec.name)
+          .setIcon(spec.icon);
+
+        if (spec.value) {
+          if (spec.value == data.value) {
+            item.setSelected(true);
+          }
+
+          var handler = function(spec, e) {
+            e.prevent();
+            menu.close();
+            updateValue(spec);
+          };
+
+          item.setHandler(JX.bind(null, handler, spec));
+        } else if (spec.href) {
+          item.setHref(spec.href);
+          item.setHandler(function() { menu.close(); });
+        } else {
+          item.setDisabled(true);
+        }
+
+        list.addItem(item);
+      }
+
+      menu.setContent(list.getNode());
+    });
+
+    menu.open();
+  });
+
+
 });