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
@@ -2639,6 +2639,7 @@
     'PhabricatorTypeaheadCompositeDatasource' => 'applications/typeahead/datasource/PhabricatorTypeaheadCompositeDatasource.php',
     'PhabricatorTypeaheadDatasource' => 'applications/typeahead/datasource/PhabricatorTypeaheadDatasource.php',
     'PhabricatorTypeaheadDatasourceController' => 'applications/typeahead/controller/PhabricatorTypeaheadDatasourceController.php',
+    'PhabricatorTypeaheadFunctionHelpController' => 'applications/typeahead/controller/PhabricatorTypeaheadFunctionHelpController.php',
     'PhabricatorTypeaheadInvalidTokenException' => 'applications/typeahead/exception/PhabricatorTypeaheadInvalidTokenException.php',
     'PhabricatorTypeaheadModularDatasourceController' => 'applications/typeahead/controller/PhabricatorTypeaheadModularDatasourceController.php',
     'PhabricatorTypeaheadMonogramDatasource' => 'applications/typeahead/datasource/PhabricatorTypeaheadMonogramDatasource.php',
@@ -6054,6 +6055,7 @@
     'PhabricatorTypeaheadCompositeDatasource' => 'PhabricatorTypeaheadDatasource',
     'PhabricatorTypeaheadDatasource' => 'Phobject',
     'PhabricatorTypeaheadDatasourceController' => 'PhabricatorController',
+    'PhabricatorTypeaheadFunctionHelpController' => 'PhabricatorTypeaheadDatasourceController',
     'PhabricatorTypeaheadInvalidTokenException' => 'Exception',
     'PhabricatorTypeaheadModularDatasourceController' => 'PhabricatorTypeaheadDatasourceController',
     'PhabricatorTypeaheadMonogramDatasource' => 'PhabricatorTypeaheadDatasource',
diff --git a/src/applications/maniphest/typeahead/ManiphestNoOwnerDatasource.php b/src/applications/maniphest/typeahead/ManiphestNoOwnerDatasource.php
--- a/src/applications/maniphest/typeahead/ManiphestNoOwnerDatasource.php
+++ b/src/applications/maniphest/typeahead/ManiphestNoOwnerDatasource.php
@@ -20,7 +20,20 @@
   public function getDatasourceFunctions() {
     return array(
       'none' => array(
-        'name' => pht('Find results which are not assigned.'),
+        'name' => pht('No Owner'),
+        'summary' => pht('Find results which are not assigned.'),
+        'description' => pht(
+          'This function includes results which have no owner. Use a query '.
+          'like this to find unassigned results:'.
+          "\n\n".
+          '> none()'.
+          "\n\n".
+          'If you combine this function with other functions, the query will '.
+          'return results which match the other selectors //or// have no '.
+          'owner. For example, this query will find results which are owned '.
+          'by `alincoln`, and will also find results which have no owner:'.
+          "\n\n".
+          '> alincoln, none()'),
       ),
     );
   }
diff --git a/src/applications/project/typeahead/PhabricatorProjectLogicalOrNotDatasource.php b/src/applications/project/typeahead/PhabricatorProjectLogicalOrNotDatasource.php
--- a/src/applications/project/typeahead/PhabricatorProjectLogicalOrNotDatasource.php
+++ b/src/applications/project/typeahead/PhabricatorProjectLogicalOrNotDatasource.php
@@ -24,10 +24,54 @@
   public function getDatasourceFunctions() {
     return array(
       'any' => array(
-        'name' => pht('Find results in any of several projects.'),
+        'name' => pht('In Any: ...'),
+        'arguments' => pht('project'),
+        'summary' => pht('Find results in any of several projects.'),
+        'description' => pht(
+          'This function allows you to find results in one of several '.
+          'projects. Another way to think of this function is that it '.
+          'allows you to perform an "or" query.'.
+          "\n\n".
+          'By default, if you enter several projects, results are returned '.
+          'only if they belong to all of the projects you enter. That is, '.
+          'this query will only return results in //both// projects:'.
+          "\n\n".
+          '> ios, android'.
+          "\n\n".
+          'If you want to find results in any of several projects, you can '.
+          'use the `any()` function. For example, you can use this query  to '.
+          'find results which are in //either// project:'.
+          "\n\n".
+          '> any(ios), any(android)'.
+          "\n\n".
+          'You can combine the `any()` function with normal project tokens '.
+          'to refine results. For example, use this query to find bugs in '.
+          '//either// iOS or Android:'.
+          "\n\n".
+          '> bug, any(ios), any(android)'),
       ),
       'not' => array(
-        'name' => pht('Find results not in specific projects.'),
+        'name' => pht('Not In: ...'),
+        'arguments' => pht('project'),
+        'summary' => pht('Find results not in specific projects.'),
+        'description' => pht(
+          'This function allows you to find results which are not in '.
+          'one or more projects. For example, use this query to find '.
+          'results which are not associated with a specific project:'.
+          "\n\n".
+          '> not(vanilla)'.
+          "\n\n".
+          'You can exclude multiple projects. This will cause the query '.
+          'to return only results which are not in any of the excluded '.
+          'projects:'.
+          "\n\n".
+          '> not(vanilla), not(chocolate)'.
+          "\n\n".
+          'You can combine this function with other functions to refine '.
+          'results. For example, use this query to find iOS results which '.
+          'are not bugs:'.
+          "\n\n".
+          '> ios, not(bug)'),
       ),
     );
   }
diff --git a/src/applications/project/typeahead/PhabricatorProjectLogicalUserDatasource.php b/src/applications/project/typeahead/PhabricatorProjectLogicalUserDatasource.php
--- a/src/applications/project/typeahead/PhabricatorProjectLogicalUserDatasource.php
+++ b/src/applications/project/typeahead/PhabricatorProjectLogicalUserDatasource.php
@@ -24,7 +24,17 @@
   public function getDatasourceFunctions() {
     return array(
       'projects' => array(
-        'name' => pht("Find results in any of a user's projects."),
+        'name' => pht('Projects: ...'),
+        'arguments' => pht('username'),
+        'summary' => pht("Find results in any of a user's projects."),
+        'description' => pht(
+          'This function allows you to find results associated with any '.
+          'of the projects a specified user is a member of. For example, '.
+          'this will find results associated with all of the projects '.
+          '`alincoln` is a member of:'.
+          "\n\n".
+          '> projects(alincoln)'.
+          "\n\n"),
       ),
     );
   }
diff --git a/src/applications/project/typeahead/PhabricatorProjectLogicalViewerDatasource.php b/src/applications/project/typeahead/PhabricatorProjectLogicalViewerDatasource.php
--- a/src/applications/project/typeahead/PhabricatorProjectLogicalViewerDatasource.php
+++ b/src/applications/project/typeahead/PhabricatorProjectLogicalViewerDatasource.php
@@ -18,7 +18,19 @@
   public function getDatasourceFunctions() {
     return array(
       'viewerprojects' => array(
-        'name' => pht("Find results in any of the current viewer's projects."),
+        'name' => pht("Current Viewer's Projects"),
+        'summary' => pht(
+          "Find results in any of the current viewer's projects."),
+        'description' => pht(
+          "This function matches results in any of the current viewing ".
+          "user's projects:".
+          "\n\n".
+          "> viewerprojects()".
+          "\n\n".
+          "This normally means //your// projects, but if you save a query ".
+          "using this function and send it to someone else, it will mean ".
+          "//their// projects when they run it (they become the currnet ".
+          "viewer). This can be useful for building dashboard panels."),
       ),
     );
   }
diff --git a/src/applications/project/typeahead/PhabricatorProjectMembersDatasource.php b/src/applications/project/typeahead/PhabricatorProjectMembersDatasource.php
--- a/src/applications/project/typeahead/PhabricatorProjectMembersDatasource.php
+++ b/src/applications/project/typeahead/PhabricatorProjectMembersDatasource.php
@@ -24,7 +24,14 @@
   public function getDatasourceFunctions() {
     return array(
       'members' => array(
-        'name' => pht('Find results for members of a project.'),
+        'name' => pht('Members: ...'),
+        'arguments' => pht('project'),
+        'summary' => pht('Find results for members of a project.'),
+        'description' => pht(
+          'This function allows you to find results for any of the members '.
+          'of a project:'.
+          "\n\n".
+          '> members(frontend)'),
       ),
     );
   }
diff --git a/src/applications/project/typeahead/PhabricatorProjectNoProjectsDatasource.php b/src/applications/project/typeahead/PhabricatorProjectNoProjectsDatasource.php
--- a/src/applications/project/typeahead/PhabricatorProjectNoProjectsDatasource.php
+++ b/src/applications/project/typeahead/PhabricatorProjectNoProjectsDatasource.php
@@ -18,7 +18,15 @@
   public function getDatasourceFunctions() {
     return array(
       'null' => array(
-        'name' => pht('Find results which are not in any projects.'),
+        'name' => pht('Not In Any Projects'),
+        'summary' => pht('Find results which are not in any projects.'),
+        'description' => pht(
+          'This function matches results which are not associated with any '.
+          'projects. It is usually most often used to find objects which '.
+          'might have slipped through the cracks and not been organized '.
+          'properly.'.
+          "\n\n".
+          "> null()"),
       ),
     );
   }
diff --git a/src/applications/typeahead/application/PhabricatorTypeaheadApplication.php b/src/applications/typeahead/application/PhabricatorTypeaheadApplication.php
--- a/src/applications/typeahead/application/PhabricatorTypeaheadApplication.php
+++ b/src/applications/typeahead/application/PhabricatorTypeaheadApplication.php
@@ -11,6 +11,8 @@
       '/typeahead/' => array(
         '(?P<action>browse|class)/(?:(?P<class>\w+)/)?'
           => 'PhabricatorTypeaheadModularDatasourceController',
+        'help/(?P<class>\w+)/'
+          => 'PhabricatorTypeaheadFunctionHelpController',
       ),
     );
   }
diff --git a/src/applications/typeahead/controller/PhabricatorTypeaheadFunctionHelpController.php b/src/applications/typeahead/controller/PhabricatorTypeaheadFunctionHelpController.php
new file mode 100644
--- /dev/null
+++ b/src/applications/typeahead/controller/PhabricatorTypeaheadFunctionHelpController.php
@@ -0,0 +1,150 @@
+<?php
+
+final class PhabricatorTypeaheadFunctionHelpController
+  extends PhabricatorTypeaheadDatasourceController {
+
+  public function shouldAllowPublic() {
+    return true;
+  }
+
+  public function handleRequest(AphrontRequest $request) {
+    $viewer = $this->getViewer();
+    $class = $request->getURIData('class');
+
+    $sources = id(new PhutilSymbolLoader())
+      ->setAncestorClass('PhabricatorTypeaheadDatasource')
+      ->loadObjects();
+    if (!isset($sources[$class])) {
+      return new Aphront404Response();
+    }
+
+    $source = $sources[$class];
+
+    $application_class = $source->getDatasourceApplicationClass();
+    if ($application_class) {
+      $result = id(new PhabricatorApplicationQuery())
+        ->setViewer($this->getViewer())
+        ->withClasses(array($application_class))
+        ->execute();
+      if (!$result) {
+        return new Aphront404Response();
+      }
+    }
+
+    $source->setViewer($viewer);
+
+    $title = pht('Typeahead Function Help');
+
+    $functions = $source->getAllDatasourceFunctions();
+    ksort($functions);
+
+    $content = array();
+
+    $content[] = '= '.pht('Overview');
+    $content[] = pht(
+      'Typeahead functions are an advanced feature which allow you to build '.
+      'more powerful queries. This document explains functions available '.
+      'for the selected control.'.
+      "\n\n".
+      'Note that different controls support //different// functions '.
+      '(depending on what the control is doing), so these specific functions '.
+      'may not work everywhere. You can always check the help for a control '.
+      'to review which functions are available for that control.');
+
+    $table = array();
+
+    $table_header = array(
+      pht('Function'),
+      pht('Token Name'),
+      pht('Summary'),
+    );
+    $table[] = '| '.implode(' | ', $table_header).' |';
+    $table[] = '|---|---|---|';
+
+    foreach ($functions as $function => $spec) {
+      $spec = $spec + array(
+        'summary' => null,
+        'arguments' => null,
+      );
+
+      if (idx($spec, 'arguments')) {
+        $signature = '**'.$function.'(**//'.$spec['arguments'].'//**)**';
+      } else {
+        $signature = '**'.$function.'()**';
+      }
+
+      $name = idx($spec, 'name', '');
+      $summary = idx($spec, 'summary', '');
+
+      $table[] = '| '.$signature.' | '.$name.' | '.$summary.' |';
+    }
+
+    $table = implode("\n", $table);
+    $content[] = '= '.pht('Function Quick Reference');
+    $content[] = pht(
+      'This table briefly describes available functions for this control. '.
+      'For details on a particular function, see the corresponding section '.
+      'below.');
+    $content[] = $table;
+
+    $content[] = '= '.pht('Using Typeahead Functions');
+    $content[] = pht(
+      'In addition to typing user and project names to build queries, you can '.
+      'also type the names of special functions which give you more options '.
+      'and the ability to express more complex queries.'.
+      "\n\n".
+      'Functions have an internal name (like `viewer()`) and a '.
+      'human-readable name, like `Current Viewer`. In general, you can type '.
+      'either one to select the function. You can also click the '.
+      '{nav icon=search} button on any typeahead control to browse available '.
+      'functions and find this documentation.'.
+      "\n\n".
+      'This documentation uses the internal names to make it clear where '.
+      'tokens begin and end. Specifically, you will find queries written '.
+      'out like this in the documentation: '.
+      "\n\n".
+      '> viewer(), alincoln'.
+      "\n\n".
+      'When this query is actually shown in the control, it will look more '.
+      'like this:'.
+      "\n\n".
+      '> {nav Current Viewer} {nav alincoln (Abraham Lincoln)}');
+
+
+    $middot = "\xC2\xB7";
+    foreach ($functions as $function => $spec) {
+      $arguments = idx($spec, 'arguments', '');
+      $name = idx($spec, 'name');
+      $content[] = '= '.$function.'('.$arguments.') '.$middot.' '.$name;
+      $content[] = $spec['description'];
+    }
+
+    $content = implode("\n\n", $content);
+
+    $content_box = PhabricatorMarkupEngine::renderOneObject(
+      id(new PhabricatorMarkupOneOff())->setContent($content),
+      'default',
+      $viewer);
+
+    $header = id(new PHUIHeaderView())
+      ->setHeader($title);
+
+    $document = id(new PHUIDocumentView())
+      ->setHeader($header)
+      ->setFontKit(PHUIDocumentView::FONT_SOURCE_SANS)
+      ->appendChild($content_box);
+
+    $crumbs = $this->buildApplicationCrumbs();
+    $crumbs->addTextCrumb(pht('Function Help'));
+
+    return $this->buildApplicationPage(
+      array(
+        $crumbs,
+        $document,
+      ),
+      array(
+        'title' => $title,
+      ));
+  }
+
+}
diff --git a/src/applications/typeahead/controller/PhabricatorTypeaheadModularDatasourceController.php b/src/applications/typeahead/controller/PhabricatorTypeaheadModularDatasourceController.php
--- a/src/applications/typeahead/controller/PhabricatorTypeaheadModularDatasourceController.php
+++ b/src/applications/typeahead/controller/PhabricatorTypeaheadModularDatasourceController.php
@@ -222,11 +222,32 @@
           $frame,
         );
 
+        $function_help = null;
+        if ($source->getAllDatasourceFunctions()) {
+          $reference_uri = '/typeahead/help/'.get_class($source).'/';
+
+          $reference_link = phutil_tag(
+            'a',
+            array(
+              'href' => $reference_uri,
+              'target' => '_blank',
+            ),
+            pht('Reference: Advanced Functions'));
+
+          $function_help = array(
+            id(new PHUIIconView())
+              ->setIconFont('fa-book'),
+            ' ',
+            $reference_link,
+          );
+        }
+
         return $this->newDialog()
           ->setWidth(AphrontDialogView::WIDTH_FORM)
           ->setRenderDialogAsDiv(true)
           ->setTitle($source->getBrowseTitle())
           ->appendChild($browser)
+          ->addFooter($function_help)
           ->addCancelButton('/', pht('Close'));
       }
 
diff --git a/src/applications/typeahead/datasource/PhabricatorTypeaheadCompositeDatasource.php b/src/applications/typeahead/datasource/PhabricatorTypeaheadCompositeDatasource.php
--- a/src/applications/typeahead/datasource/PhabricatorTypeaheadCompositeDatasource.php
+++ b/src/applications/typeahead/datasource/PhabricatorTypeaheadCompositeDatasource.php
@@ -117,6 +117,14 @@
     return $this->usable;
   }
 
+  public function getAllDatasourceFunctions() {
+    $results = parent::getAllDatasourceFunctions();
+    foreach ($this->getUsableDatasources() as $source) {
+      $results += $source->getAllDatasourceFunctions();
+    }
+    return $results;
+  }
+
   protected function didEvaluateTokens(array $results) {
     foreach ($this->getUsableDatasources() as $source) {
       $results = $source->didEvaluateTokens($results);
diff --git a/src/applications/typeahead/datasource/PhabricatorTypeaheadDatasource.php b/src/applications/typeahead/datasource/PhabricatorTypeaheadDatasource.php
--- a/src/applications/typeahead/datasource/PhabricatorTypeaheadDatasource.php
+++ b/src/applications/typeahead/datasource/PhabricatorTypeaheadDatasource.php
@@ -279,6 +279,14 @@
   /**
    * @task functions
    */
+  public function getAllDatasourceFunctions() {
+    return $this->getDatasourceFunctions();
+  }
+
+
+  /**
+   * @task functions
+   */
   protected function canEvaluateFunction($function) {
     return $this->shouldStripFunction($function);
   }