diff --git a/src/applications/project/query/PhabricatorProjectSearchEngine.php b/src/applications/project/query/PhabricatorProjectSearchEngine.php
--- a/src/applications/project/query/PhabricatorProjectSearchEngine.php
+++ b/src/applications/project/query/PhabricatorProjectSearchEngine.php
@@ -13,8 +13,7 @@
 
   public function newQuery() {
     return id(new PhabricatorProjectQuery())
-      ->needImages(true)
-      ->withIsMilestone(false);
+      ->needImages(true);
   }
 
   protected function buildCustomSearchFields() {
@@ -34,6 +33,17 @@
         ->setLabel(pht('Status'))
         ->setKey('status')
         ->setOptions($this->getStatusOptions()),
+      id(new PhabricatorSearchThreeStateField())
+        ->setLabel(pht('Milestones'))
+        ->setKey('isMilestone')
+        ->setOptions(
+          pht('(Show All)'),
+          pht('Show Only Milestones'),
+          pht('Hide Milestones'))
+        ->setDescription(
+          pht(
+            'Pass true to find only milestones, or false to omit '.
+            'milestones.')),
       id(new PhabricatorSearchCheckboxesField())
         ->setLabel(pht('Icons'))
         ->setKey('icons')
@@ -77,6 +87,10 @@
       $query->withColors($map['colors']);
     }
 
+    if ($map['isMilestone'] !== null) {
+      $query->withIsMilestone($map['isMilestone']);
+    }
+
     return $query;
   }
 
@@ -103,6 +117,9 @@
 
     $viewer_phid = $this->requireViewer()->getPHID();
 
+    // By default, do not show milestones in the list view.
+    $query->setParameter('isMilestone', false);
+
     switch ($query_key) {
       case 'all':
         return $query;
diff --git a/src/applications/project/storage/PhabricatorProject.php b/src/applications/project/storage/PhabricatorProject.php
--- a/src/applications/project/storage/PhabricatorProject.php
+++ b/src/applications/project/storage/PhabricatorProject.php
@@ -742,6 +742,10 @@
         ->setType('string')
         ->setDescription(pht('Primary slug/hashtag.')),
       id(new PhabricatorConduitSearchFieldSpecification())
+        ->setKey('milestone')
+        ->setType('int?')
+        ->setDescription(pht('For milestones, milestone sequence number.')),
+      id(new PhabricatorConduitSearchFieldSpecification())
         ->setKey('icon')
         ->setType('map<string, wild>')
         ->setDescription(pht('Information about the project icon.')),
@@ -756,9 +760,16 @@
     $color_key = $this->getColor();
     $color_name = PhabricatorProjectIconSet::getColorName($color_key);
 
+    if ($this->isMilestone()) {
+      $milestone = (int)$this->getMilestoneNumber();
+    } else {
+      $milestone = null;
+    }
+
     return array(
       'name' => $this->getName(),
       'slug' => $this->getPrimarySlug(),
+      'milestone' => $milestone,
       'icon' => array(
         'key' => $this->getDisplayIconKey(),
         'name' => $this->getDisplayIconName(),