diff --git a/src/__celerity_resource_map__.php b/src/__celerity_resource_map__.php
index 840a4c1455..412e0e63b2 100644
--- a/src/__celerity_resource_map__.php
+++ b/src/__celerity_resource_map__.php
@@ -35,6 +35,13 @@ celerity_register_resource_map(array(
     'disk' => '/rsrc/image/credit_cards.png',
     'type' => 'png',
   ),
+  '/rsrc/image/divot.png' =>
+  array(
+    'hash' => '3be267bd11ea375bf68e808893718e0e',
+    'uri' => '/res/3be267bd/rsrc/image/divot.png',
+    'disk' => '/rsrc/image/divot.png',
+    'type' => 'png',
+  ),
   '/rsrc/image/glyph_sprite.png' =>
   array(
     'hash' => '0a1ea7c048be9f0b76ab2c807a9a1c0d',
@@ -1402,6 +1409,20 @@ celerity_register_resource_map(array(
     ),
     'disk' => '/rsrc/js/application/core/behavior-keyboard-shortcuts.js',
   ),
+  'javelin-behavior-phabricator-nav' =>
+  array(
+    'uri' => '/res/adaae8ae/rsrc/js/application/core/behavior-phabricator-nav.js',
+    'type' => 'js',
+    'requires' =>
+    array(
+      0 => 'javelin-behavior',
+      1 => 'javelin-stratcom',
+      2 => 'javelin-dom',
+      3 => 'javelin-magical-init',
+      4 => 'javelin-vector',
+    ),
+    'disk' => '/rsrc/js/application/core/behavior-phabricator-nav.js',
+  ),
   'javelin-behavior-phabricator-notification-example' =>
   array(
     'uri' => '/res/df97e4b3/rsrc/js/application/uiexample/notification-example.js',
@@ -2285,6 +2306,15 @@ celerity_register_resource_map(array(
     ),
     'disk' => '/rsrc/js/application/core/DropdownMenuItem.js',
   ),
+  'phabricator-nav-view-css' =>
+  array(
+    'uri' => '/res/3443576d/rsrc/css/aphront/phabricator-nav-view.css',
+    'type' => 'css',
+    'requires' =>
+    array(
+    ),
+    'disk' => '/rsrc/css/aphront/phabricator-nav-view.css',
+  ),
   'phabricator-notification' =>
   array(
     'uri' => '/res/cacd79f1/rsrc/js/application/core/Notification.js',
diff --git a/src/view/layout/AphrontSideNavFilterView.php b/src/view/layout/AphrontSideNavFilterView.php
index aa36c9a450..c7f247599a 100644
--- a/src/view/layout/AphrontSideNavFilterView.php
+++ b/src/view/layout/AphrontSideNavFilterView.php
@@ -40,6 +40,18 @@ final class AphrontSideNavFilterView extends AphrontView {
   private $items = array();
   private $baseURI;
   private $selectedFilter = false;
+  private $flexNav;
+  private $flexible;
+
+  public function setFlexNav($flex_nav) {
+    $this->flexNav = $flex_nav;
+    return $this;
+  }
+
+  public function setFlexible($flexible) {
+    $this->flexible = $flexible;
+    return $this;
+  }
 
   public function addFilter($key, $name, $uri = null, $relative = false) {
     $this->items[] = array(
@@ -102,6 +114,8 @@ final class AphrontSideNavFilterView extends AphrontView {
     }
 
     $view = new AphrontSideNavView();
+    $view->setFlexNav($this->flexNav);
+    $view->setFlexible($this->flexible);
     foreach ($this->items as $item) {
       list($type, $key, $name) = $item;
       switch ($type) {
diff --git a/src/view/layout/AphrontSideNavView.php b/src/view/layout/AphrontSideNavView.php
index 6a2d52573a..6a43eee791 100644
--- a/src/view/layout/AphrontSideNavView.php
+++ b/src/view/layout/AphrontSideNavView.php
@@ -1,7 +1,7 @@
 <?php
 
 /*
- * Copyright 2011 Facebook, Inc.
+ * Copyright 2012 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,29 +19,88 @@
 final class AphrontSideNavView extends AphrontView {
 
   protected $items = array();
+  protected $flexNav;
+  protected $isFlexible;
 
   public function addNavItem($item) {
     $this->items[] = $item;
     return $this;
   }
 
+  public function setFlexNav($flex) {
+    $this->flexNav = $flex;
+    return $this;
+  }
+
+  public function setFlexible($flexible) {
+    $this->flexible = $flexible;
+    return $this;
+  }
+
   public function render() {
     $view = new AphrontNullView();
     $view->appendChild($this->items);
 
-    require_celerity_resource('aphront-side-nav-view-css');
+    if ($this->flexNav) {
+      require_celerity_resource('phabricator-nav-view-css');
 
-    return
-      '<table class="aphront-side-nav-view">'.
-        '<tr>'.
-          '<th class="aphront-side-nav-navigation">'.
-            $view->render().
-          '</th>'.
-          '<td class="aphront-side-nav-content">'.
-            $this->renderChildren().
-          '</td>'.
-        '</tr>'.
-      '</table>';
+      $nav_id = celerity_generate_unique_node_id();
+      $drag_id = celerity_generate_unique_node_id();
+      $content_id = celerity_generate_unique_node_id();
+
+      if ($this->flexible) {
+        Javelin::initBehavior(
+          'phabricator-nav',
+          array(
+            'navID'     => $nav_id,
+            'dragID'    => $drag_id,
+            'contentID' => $content_id,
+          ));
+        $flex_bar = phutil_render_tag(
+          'div',
+          array(
+            'class' => 'phabricator-nav-drag',
+            'id' => $drag_id,
+          ),
+          '');
+      } else {
+        $flex_bar = null;
+      }
+
+      return
+        '<div class="phabricator-nav">'.
+          phutil_render_tag(
+            'div',
+            array(
+              'class' => 'phabricator-nav-col',
+              'id'    => $nav_id,
+            ),
+            $view->render()).
+          $flex_bar.
+          phutil_render_tag(
+            'div',
+            array(
+              'class' => 'phabricator-nav-content',
+              'id' => $content_id,
+            ),
+            $this->renderChildren()).
+        '</div>';
+    } else {
+
+      require_celerity_resource('aphront-side-nav-view-css');
+
+      return
+        '<table class="aphront-side-nav-view">'.
+          '<tr>'.
+            '<th class="aphront-side-nav-navigation">'.
+              $view->render().
+            '</th>'.
+            '<td class="aphront-side-nav-content">'.
+              $this->renderChildren().
+            '</td>'.
+          '</tr>'.
+        '</table>';
+    }
   }
 
 }
diff --git a/webroot/rsrc/css/aphront/phabricator-nav-view.css b/webroot/rsrc/css/aphront/phabricator-nav-view.css
new file mode 100644
index 0000000000..fecb298970
--- /dev/null
+++ b/webroot/rsrc/css/aphront/phabricator-nav-view.css
@@ -0,0 +1,83 @@
+/**
+ * @provides phabricator-nav-view-css
+ */
+
+.jx-drag-col {
+  cursor: col-resize;
+}
+
+.phabricator-nav-col {
+  position: fixed;
+  top: 44px;
+  left: 0;
+  bottom: 0;
+  width: 179px;
+
+  background: #e3e3e3;
+  border-right: 1px solid #999c9e;
+  box-shadow: inset 0 0 10px rgba(0, 0, 0, 0.20);
+
+  overflow-y: auto;
+  overflow-x: hidden;
+
+  white-space: nowrap;
+}
+
+.phabricator-nav-drag {
+  position: fixed;
+  top: 44px;
+  left: 177px;
+  width: 7px;
+  bottom: 0;
+  z-index: 5;
+
+  cursor: col-resize;
+  background: #f5f5f5;
+  border-style: solid;
+  border-width: 0 1px 0 1px;
+  border-color: #fff #999c9e #fff #999c9e;
+
+  box-shadow: inset -1px 0px 2px rgba(0, 0, 0, 0.15);
+
+  background-image: url(/rsrc/image/divot.png);
+  background-position: center;
+  background-repeat: no-repeat;
+}
+
+.device-tablet .phabricator-nav-drag,
+.device-phone .phabricator-nav-drag {
+  display: none;
+}
+
+.phabricator-nav-col a,
+.phabricator-nav-col span {
+  display: block;
+}
+
+.phabricator-nav-content {
+  margin-left: 180px;
+}
+
+
+.phabricator-nav-col span {
+  display: block;
+  font-weight: bold;
+  padding: 6px 6px 6px 12px;
+  color: #222222;
+}
+
+.phabricator-nav-col a {
+  display: block;
+  padding: 3px 6px 3px 24px;
+  font-weight: bold;
+  text-decoration: none;
+}
+
+.phabricator-nav-col a.aphront-side-nav-selected {
+  background: #a1bbe5;
+}
+
+.phabricator-nav-col a:hover {
+  background: #3875d7;
+  color: #ffffff;
+}
diff --git a/webroot/rsrc/image/divot.png b/webroot/rsrc/image/divot.png
new file mode 100644
index 0000000000..d3c885483e
Binary files /dev/null and b/webroot/rsrc/image/divot.png differ
diff --git a/webroot/rsrc/js/application/core/behavior-phabricator-nav.js b/webroot/rsrc/js/application/core/behavior-phabricator-nav.js
new file mode 100644
index 0000000000..c1c182f122
--- /dev/null
+++ b/webroot/rsrc/js/application/core/behavior-phabricator-nav.js
@@ -0,0 +1,97 @@
+/**
+ * @provides javelin-behavior-phabricator-nav
+ * @requires javelin-behavior
+ *           javelin-stratcom
+ *           javelin-dom
+ *           javelin-magical-init
+ *           javelin-vector
+ * @javelin
+ */
+
+JX.behavior('phabricator-nav', function(config) {
+
+  var dragging;
+  var track;
+
+  var nav = JX.$(config.navID);
+  var drag = JX.$(config.dragID);
+  var content = JX.$(config.contentID);
+
+  JX.enableDispatch(document.body, 'mousemove');
+
+  JX.DOM.listen(drag, 'mousedown', null, function(e) {
+    dragging = JX.$V(e);
+
+    // Show the "col-resize" cursor on the whole document while we're
+    // dragging, since the mouse will slip off the actual bar fairly often and
+    // we don't want it to flicker.
+    JX.DOM.alterClass(document.body, 'jx-drag-col', true);
+
+    track = [
+      {
+        element: nav,
+        parameter: 'width',
+        start: JX.Vector.getDim(nav).x,
+        scale: 1,
+
+        width: JX.Vector.getDim(nav).x,
+        minWidth: 150,
+        minScale: 1
+      },
+      {
+        element: drag,
+        parameter: 'left',
+        start: JX.$V(drag).x,
+        scale: 1
+      },
+      {
+        element: content,
+        parameter: 'marginLeft',
+        start: parseInt(getComputedStyle(content).marginLeft, 10),
+        scale: 1,
+
+        width: JX.Vector.getDim(content).x,
+        minWidth: 300,
+        minScale: -1
+      }
+    ];
+
+    e.kill();
+  });
+
+  JX.Stratcom.listen('mousemove', null, function(e) {
+    if (!dragging) {
+      return;
+    }
+
+    var dx = JX.$V(e).x - dragging.x;
+    var panel;
+
+    for (var k = 0; k < track.length; k++) {
+      panel = track[k];
+      if (!panel.minWidth) {
+        continue;
+      }
+      var new_width = panel.width + (dx * panel.minScale);
+      if (new_width < panel.minWidth) {
+        dx = (panel.minWidth - panel.width) * panel.minScale;
+      }
+    }
+
+    for (var k = 0; k < track.length; k++) {
+      panel = track[k];
+      var v = (panel.start + (dx * panel.scale));
+      panel.element.style[panel.parameter] = v + 'px';
+    }
+  });
+
+  JX.Stratcom.listen('mouseup', null, function(e) {
+    if (!dragging) {
+      return;
+    }
+
+    JX.DOM.alterClass(document.body, 'jx-drag-col', false);
+    dragging = false;
+  });
+
+});