Index: src/__celerity_resource_map__.php
===================================================================
--- src/__celerity_resource_map__.php
+++ src/__celerity_resource_map__.php
@@ -2267,7 +2267,7 @@
   ),
   'javelin-behavior-policy-control' =>
   array(
-    'uri' => '/res/f43ba427/rsrc/js/application/policy/behavior-policy-control.js',
+    'uri' => '/res/ce9f54c8/rsrc/js/application/policy/behavior-policy-control.js',
     'type' => 'js',
     'requires' =>
     array(
@@ -2276,6 +2276,7 @@
       2 => 'javelin-util',
       3 => 'phabricator-dropdown-menu',
       4 => 'phabricator-menu-item',
+      5 => 'javelin-workflow',
     ),
     'disk' => '/rsrc/js/application/policy/behavior-policy-control.js',
   ),
Index: src/view/form/control/AphrontFormPolicyControl.php
===================================================================
--- src/view/form/control/AphrontFormPolicyControl.php
+++ src/view/form/control/AphrontFormPolicyControl.php
@@ -54,6 +54,48 @@
         'icon' => $policy->getIcon(),
       );
     }
+
+    // If we were passed several custom policy options, throw away the ones
+    // which aren't the value for this capability. For example, an object might
+    // have a custom view pollicy and a custom edit policy. When we render
+    // the selector for "Can View", we don't want to show the "Can Edit"
+    // custom policy -- if we did, the menu would look like this:
+    //
+    //   Custom
+    //     Custom Policy
+    //     Custom Policy
+    //
+    // ...where one is the "view" custom policy, and one is the "edit" custom
+    // policy.
+
+    $type_custom = PhabricatorPolicyType::TYPE_CUSTOM;
+    if (!empty($options[$type_custom])) {
+      $options[$type_custom] = array_select_keys(
+        $options[$type_custom],
+        array($this->getValue()));
+    }
+
+    // If there aren't any custom policies, add a placeholder policy so we
+    // render a menu item. This allows the user to switch to a custom policy.
+
+    if (empty($options[$type_custom])) {
+      $placeholder = new PhabricatorPolicy();
+      $placeholder->setName(pht('Custom Policy...'));
+      $options[$type_custom][$this->getCustomPolicyPlaceholder()] = array(
+        'name' => $placeholder->getName(),
+        'full' => $placeholder->getName(),
+        'icon' => $placeholder->getIcon(),
+      );
+    }
+
+    $options = array_select_keys(
+      $options,
+      array(
+        PhabricatorPolicyType::TYPE_GLOBAL,
+        PhabricatorPolicyType::TYPE_CUSTOM,
+        PhabricatorPolicyType::TYPE_PROJECT,
+      ));
+
     return $options;
   }
 
@@ -121,6 +163,7 @@
         'icons' => $icons,
         'labels' => $labels,
         'value' => $this->getValue(),
+        'customPlaceholder' => $this->getCustomPolicyPlaceholder(),
       ));
 
     $selected = $flat_options[$this->getValue()];
@@ -165,5 +208,8 @@
       ));
   }
 
+  private function getCustomPolicyPlaceholder() {
+    return 'custom:placeholder';
+  }
 
 }
Index: webroot/rsrc/js/application/policy/behavior-policy-control.js
===================================================================
--- webroot/rsrc/js/application/policy/behavior-policy-control.js
+++ webroot/rsrc/js/application/policy/behavior-policy-control.js
@@ -5,6 +5,7 @@
  *           javelin-util
  *           phabricator-dropdown-menu
  *           phabricator-menu-item
+ *           javelin-workflow
  * @javelin
  */
 JX.behavior('policy-control', function(config) {
@@ -23,25 +24,37 @@
     for (var ii = 0; ii < config.groups.length; ii++) {
       var group = config.groups[ii];
 
-      var header = new JX.PhabricatorMenuItem(config.labels[group]);
+      var header = new JX.PhabricatorMenuItem(config.labels[group], JX.bag);
       header.setDisabled(true);
       menu.addItem(header);
 
       for (var jj = 0; jj < config.order[group].length; jj++) {
         var phid = config.order[group][jj];
-        var option = config.options[phid];
 
-        var render = [JX.$H(config.icons[option.icon]), option.name];
+        var onselect;
+        if (group == 'custom') {
+          onselect = JX.bind(null, function(phid) {
+            var uri = get_custom_uri(phid);
+
+            new JX.Workflow(uri)
+              .setHandler(function(response) {
+                if (!response.phid) {
+                  return;
+                }
+
+                replace_policy(phid, response.phid, response.info);
+                select_policy(response.phid);
+              })
+              .start();
+
+          }, phid);
+        } else {
+          onselect = JX.bind(null, select_policy, phid);
+        }
 
         var item = new JX.PhabricatorMenuItem(
-          render,
-          JX.bind(null, function(phid, render) {
-            JX.DOM.setContent(
-              JX.DOM.find(control, 'span', 'policy-label'),
-              render);
-            input.value = phid;
-            value = phid;
-          }, phid, render));
+          render_option(phid, true),
+          onselect);
 
         if (phid == value) {
           item.setSelected(true);
@@ -53,4 +66,56 @@
 
   });
 
+
+  var select_policy = function(phid) {
+    JX.DOM.setContent(
+      JX.DOM.find(control, 'span', 'policy-label'),
+      render_option(phid));
+
+    input.value = phid;
+    value = phid;
+  };
+
+
+  var render_option = function(phid, with_title) {
+    var option = config.options[phid];
+
+    var name = option.name;
+    if (with_title && (option.full != option.name)) {
+      name = JX.$N('span', {title: option.full}, name);
+    }
+
+    return [JX.$H(config.icons[option.icon]), name];
+  };
+
+
+  /**
+   * Get the workflow URI to create or edit a policy with a given PHID.
+   */
+  var get_custom_uri = function(phid) {
+    var uri = '/policy/edit/';
+    if (phid != config.customPlaceholder) {
+      uri += phid + '/';
+    }
+    return uri;
+  };
+
+
+  /**
+   * Replace an existing policy option with a new one. Used to swap out custom
+   * policies after the user edits them.
+   */
+  var replace_policy = function(old_phid, new_phid, info) {
+    config.options[new_phid] = info;
+    for (var k in config.order) {
+      for (var ii = 0; ii < config.order[k].length; ii++) {
+        if (config.order[k][ii] == old_phid) {
+          config.order[k][ii] = new_phid;
+          return;
+        }
+      }
+    }
+  };
+
+
 });