diff --git a/resources/sql/autopatches/20151221.search.1.version.sql b/resources/sql/autopatches/20151221.search.1.version.sql
new file mode 100644
--- /dev/null
+++ b/resources/sql/autopatches/20151221.search.1.version.sql
@@ -0,0 +1,7 @@
+CREATE TABLE {$NAMESPACE}_search.search_indexversion (
+  id INT UNSIGNED NOT NULL PRIMARY KEY AUTO_INCREMENT,
+  objectPHID VARBINARY(64) NOT NULL,
+  extensionKey VARCHAR(64) NOT NULL COLLATE {$COLLATE_TEXT},
+  version VARCHAR(128) NOT NULL COLLATE {$COLLATE_TEXT},
+  UNIQUE KEY `key_object` (objectPHID, extensionKey)
+) ENGINE=InnoDB, COLLATE {$COLLATE_TEXT};
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
@@ -3040,6 +3040,8 @@
     'PhabricatorSearchEngineTestCase' => 'applications/search/engine/__tests__/PhabricatorSearchEngineTestCase.php',
     'PhabricatorSearchField' => 'applications/search/field/PhabricatorSearchField.php',
     'PhabricatorSearchHovercardController' => 'applications/search/controller/PhabricatorSearchHovercardController.php',
+    'PhabricatorSearchIndexVersion' => 'applications/search/storage/PhabricatorSearchIndexVersion.php',
+    'PhabricatorSearchIndexVersionDestructionEngineExtension' => 'applications/search/engineextension/PhabricatorSearchIndexVersionDestructionEngineExtension.php',
     'PhabricatorSearchManagementIndexWorkflow' => 'applications/search/management/PhabricatorSearchManagementIndexWorkflow.php',
     'PhabricatorSearchManagementInitWorkflow' => 'applications/search/management/PhabricatorSearchManagementInitWorkflow.php',
     'PhabricatorSearchManagementWorkflow' => 'applications/search/management/PhabricatorSearchManagementWorkflow.php',
@@ -7403,6 +7405,8 @@
     'PhabricatorSearchEngineTestCase' => 'PhabricatorTestCase',
     'PhabricatorSearchField' => 'Phobject',
     'PhabricatorSearchHovercardController' => 'PhabricatorSearchBaseController',
+    'PhabricatorSearchIndexVersion' => 'PhabricatorSearchDAO',
+    'PhabricatorSearchIndexVersionDestructionEngineExtension' => 'PhabricatorDestructionEngineExtension',
     'PhabricatorSearchManagementIndexWorkflow' => 'PhabricatorSearchManagementWorkflow',
     'PhabricatorSearchManagementInitWorkflow' => 'PhabricatorSearchManagementWorkflow',
     'PhabricatorSearchManagementWorkflow' => 'PhabricatorManagementWorkflow',
diff --git a/src/applications/search/engineextension/PhabricatorFulltextIndexEngineExtension.php b/src/applications/search/engineextension/PhabricatorFulltextIndexEngineExtension.php
--- a/src/applications/search/engineextension/PhabricatorFulltextIndexEngineExtension.php
+++ b/src/applications/search/engineextension/PhabricatorFulltextIndexEngineExtension.php
@@ -9,6 +9,23 @@
     return pht('Fulltext Engine');
   }
 
+  public function getIndexVersion($object) {
+    $version = array();
+
+    if ($object instanceof PhabricatorApplicationTransactionInterface) {
+      // If this is a normal object with transactions, we only need to
+      // reindex it if there are new transactions (or comment edits).
+      $version[] = $this->getTransactionVersion($object);
+      $version[] = $this->getCommentVersion($object);
+    }
+
+    if (!$version) {
+      return null;
+    }
+
+    return implode(':', $version);
+  }
+
   public function shouldIndexObject($object) {
     return ($object instanceof PhabricatorFulltextInterface);
   }
@@ -27,4 +44,46 @@
     $engine->buildFulltextIndexes();
   }
 
+  private function getTransactionVersion($object) {
+    $xaction = $object->getApplicationTransactionTemplate();
+
+    $xaction_row = queryfx_one(
+      $xaction->establishConnection('r'),
+      'SELECT id FROM %T WHERE objectPHID = %s
+        ORDER BY id DESC LIMIT 1',
+      $xaction->getTableName(),
+      $object->getPHID());
+    if (!$xaction_row) {
+      return 'none';
+    }
+
+    return $xaction_row['id'];
+  }
+
+  private function getCommentVersion($object) {
+    $xaction = $object->getApplicationTransactionTemplate();
+
+    try {
+      $comment = $xaction->getApplicationTransactionCommentObject();
+    } catch (Exception $ex) {
+      return 'none';
+    }
+
+    $comment_row = queryfx_one(
+      $comment->establishConnection('r'),
+      'SELECT c.id FROM %T x JOIN %T c
+        ON x.phid = c.transactionPHID
+        WHERE x.objectPHID = %s
+        ORDER BY c.id DESC LIMIT 1',
+      $xaction->getTableName(),
+      $comment->getTableName(),
+      $object->getPHID());
+    if (!$comment_row) {
+      return 'none';
+    }
+
+    return $comment_row['id'];
+  }
+
+
 }
diff --git a/src/applications/search/engineextension/PhabricatorSearchIndexVersionDestructionEngineExtension.php b/src/applications/search/engineextension/PhabricatorSearchIndexVersionDestructionEngineExtension.php
new file mode 100644
--- /dev/null
+++ b/src/applications/search/engineextension/PhabricatorSearchIndexVersionDestructionEngineExtension.php
@@ -0,0 +1,25 @@
+<?php
+
+final class PhabricatorSearchIndexVersionDestructionEngineExtension
+  extends PhabricatorDestructionEngineExtension {
+
+  const EXTENSIONKEY = 'search.index.version';
+
+  public function getExtensionName() {
+    return pht('Search Index Versions');
+  }
+
+  public function destroyObject(
+    PhabricatorDestructionEngine $engine,
+    $object) {
+
+    $table = new PhabricatorSearchIndexVersion();
+
+    queryfx(
+      $table->establishConnection('w'),
+      'DELETE FROM %T WHERE objectPHID = %s',
+      $table->getTableName(),
+      $object->getPHID());
+  }
+
+}
diff --git a/src/applications/search/index/PhabricatorIndexEngine.php b/src/applications/search/index/PhabricatorIndexEngine.php
--- a/src/applications/search/index/PhabricatorIndexEngine.php
+++ b/src/applications/search/index/PhabricatorIndexEngine.php
@@ -45,8 +45,8 @@
     if (idx($parameters, 'force')) {
       $current_versions = array();
     } else {
-      // TODO: Load current indexed versions.
-      $current_versions = array();
+      $keys = array_keys($versions);
+      $current_versions = $this->loadIndexVersions($keys);
     }
 
     foreach ($versions as $key => $version) {
@@ -78,7 +78,7 @@
       $extension->indexObject($this, $object);
     }
 
-    // TODO: Save new index versions.
+    $this->saveIndexVersions($this->versions);
 
     return $this;
   }
@@ -96,4 +96,55 @@
     return $extensions;
   }
 
+  private function loadIndexVersions(array $extension_keys) {
+    if (!$extension_keys) {
+      return array();
+    }
+
+    $object = $this->getObject();
+    $object_phid = $object->getPHID();
+
+    $table = new PhabricatorSearchIndexVersion();
+    $conn_r = $table->establishConnection('w');
+
+    $rows = queryfx_all(
+      $conn_r,
+      'SELECT * FROM %T WHERE objectPHID = %s AND extensionKey IN (%Ls)',
+      $table->getTableName(),
+      $object_phid,
+      $extension_keys);
+
+    return ipull($rows, 'version', 'extensionKey');
+  }
+
+  private function saveIndexVersions(array $versions) {
+    if (!$versions) {
+      return;
+    }
+
+    $object = $this->getObject();
+    $object_phid = $object->getPHID();
+
+    $table = new PhabricatorSearchIndexVersion();
+    $conn_w = $table->establishConnection('w');
+
+    $sql = array();
+    foreach ($versions as $key => $version) {
+      $sql[] = qsprintf(
+        $conn_w,
+        '(%s, %s, %s)',
+        $object_phid,
+        $key,
+        $version);
+    }
+
+    queryfx(
+      $conn_w,
+      'INSERT INTO %T (objectPHID, extensionKey, version)
+        VALUES %Q
+        ON DUPLICATE KEY UPDATE version = VALUES(version)',
+      $table->getTableName(),
+      implode(', ', $sql));
+  }
+
 }
diff --git a/src/applications/search/storage/PhabricatorSearchIndexVersion.php b/src/applications/search/storage/PhabricatorSearchIndexVersion.php
new file mode 100644
--- /dev/null
+++ b/src/applications/search/storage/PhabricatorSearchIndexVersion.php
@@ -0,0 +1,26 @@
+<?php
+
+final class PhabricatorSearchIndexVersion
+  extends PhabricatorSearchDAO {
+
+  protected $objectPHID;
+  protected $extensionKey;
+  protected $version;
+
+  protected function getConfiguration() {
+    return array(
+      self::CONFIG_TIMESTAMPS => false,
+      self::CONFIG_COLUMN_SCHEMA => array(
+        'extensionKey' => 'text64',
+        'version' => 'text128',
+      ),
+      self::CONFIG_KEY_SCHEMA => array(
+        'key_object' => array(
+          'columns' => array('objectPHID', 'extensionKey'),
+          'unique' => true,
+        ),
+      ),
+    ) + parent::getConfiguration();
+  }
+
+}