diff --git a/resources/sql/autopatches/20180509.repo_identity.commits.sql b/resources/sql/autopatches/20180509.repo_identity.commits.sql
new file mode 100644
--- /dev/null
+++ b/resources/sql/autopatches/20180509.repo_identity.commits.sql
@@ -0,0 +1,3 @@
+ALTER TABLE {$NAMESPACE}_repository.repository_commit
+  ADD COLUMN authorIdentityPHID VARBINARY(64) DEFAULT NULL,
+  ADD COLUMN committerIdentityPHID VARBINARY(64) DEFAULT NULL;
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
@@ -815,8 +815,12 @@
     'DiffusionHistoryTableView' => 'applications/diffusion/view/DiffusionHistoryTableView.php',
     'DiffusionHistoryView' => 'applications/diffusion/view/DiffusionHistoryView.php',
     'DiffusionHovercardEngineExtension' => 'applications/diffusion/engineextension/DiffusionHovercardEngineExtension.php',
+    'DiffusionIdentityAssigneeDatasource' => 'applications/diffusion/typeahead/DiffusionIdentityAssigneeDatasource.php',
+    'DiffusionIdentityAssigneeEditField' => 'applications/diffusion/editfield/DiffusionIdentityAssigneeEditField.php',
+    'DiffusionIdentityAssigneeSearchField' => 'applications/diffusion/searchfield/DiffusionIdentityAssigneeSearchField.php',
     'DiffusionIdentityEditController' => 'applications/diffusion/controller/DiffusionIdentityEditController.php',
     'DiffusionIdentityListController' => 'applications/diffusion/controller/DiffusionIdentityListController.php',
+    'DiffusionIdentityUnassignedDatasource' => 'applications/diffusion/typeahead/DiffusionIdentityUnassignedDatasource.php',
     'DiffusionIdentityViewController' => 'applications/diffusion/controller/DiffusionIdentityViewController.php',
     'DiffusionInlineCommentController' => 'applications/diffusion/controller/DiffusionInlineCommentController.php',
     'DiffusionInlineCommentPreviewController' => 'applications/diffusion/controller/DiffusionInlineCommentPreviewController.php',
@@ -4092,6 +4096,7 @@
     'PhabricatorRepositoryGraphStream' => 'applications/repository/daemon/PhabricatorRepositoryGraphStream.php',
     'PhabricatorRepositoryIdentity' => 'applications/repository/storage/PhabricatorRepositoryIdentity.php',
     'PhabricatorRepositoryIdentityAssignTransaction' => 'applications/repository/xaction/PhabricatorRepositoryIdentityAssignTransaction.php',
+    'PhabricatorRepositoryIdentityChangeWorker' => 'applications/repository/worker/PhabricatorRepositoryIdentityChangeWorker.php',
     'PhabricatorRepositoryIdentityEditEngine' => 'applications/repository/engine/PhabricatorRepositoryIdentityEditEngine.php',
     'PhabricatorRepositoryIdentityFerretEngine' => 'applications/repository/search/PhabricatorRepositoryIdentityFerretEngine.php',
     'PhabricatorRepositoryIdentityPHIDType' => 'applications/repository/phid/PhabricatorRepositoryIdentityPHIDType.php',
@@ -6166,8 +6171,12 @@
     'DiffusionHistoryTableView' => 'DiffusionHistoryView',
     'DiffusionHistoryView' => 'DiffusionView',
     'DiffusionHovercardEngineExtension' => 'PhabricatorHovercardEngineExtension',
+    'DiffusionIdentityAssigneeDatasource' => 'PhabricatorTypeaheadCompositeDatasource',
+    'DiffusionIdentityAssigneeEditField' => 'PhabricatorTokenizerEditField',
+    'DiffusionIdentityAssigneeSearchField' => 'PhabricatorSearchTokenizerField',
     'DiffusionIdentityEditController' => 'DiffusionController',
     'DiffusionIdentityListController' => 'DiffusionController',
+    'DiffusionIdentityUnassignedDatasource' => 'PhabricatorTypeaheadDatasource',
     'DiffusionIdentityViewController' => 'DiffusionController',
     'DiffusionInlineCommentController' => 'PhabricatorInlineCommentController',
     'DiffusionInlineCommentPreviewController' => 'PhabricatorInlineCommentPreviewController',
@@ -10000,6 +10009,7 @@
       'PhabricatorApplicationTransactionInterface',
     ),
     'PhabricatorRepositoryIdentityAssignTransaction' => 'PhabricatorRepositoryIdentityTransactionType',
+    'PhabricatorRepositoryIdentityChangeWorker' => 'PhabricatorWorker',
     'PhabricatorRepositoryIdentityEditEngine' => 'PhabricatorEditEngine',
     'PhabricatorRepositoryIdentityFerretEngine' => 'PhabricatorFerretEngine',
     'PhabricatorRepositoryIdentityPHIDType' => 'PhabricatorPHIDType',
diff --git a/src/applications/diffusion/controller/DiffusionIdentityViewController.php b/src/applications/diffusion/controller/DiffusionIdentityViewController.php
--- a/src/applications/diffusion/controller/DiffusionIdentityViewController.php
+++ b/src/applications/diffusion/controller/DiffusionIdentityViewController.php
@@ -104,13 +104,13 @@
     }
     $properties->addProperty(
       pht('Effective User'),
-      $viewer->renderHandle($effective_phid));
+      $this->buildPropertyValue($effective_phid));
     $properties->addProperty(
       pht('Automatically Detected User'),
-      $viewer->renderHandle($automatic_phid));
+      $this->buildPropertyValue($automatic_phid));
     $properties->addProperty(
       pht('Manually Set User'),
-      $viewer->renderHandle($manual_phid));
+      $this->buildPropertyValue($manual_phid));
 
     $header = id(new PHUIHeaderView())
       ->setHeader(array(pht('Identity Assignments'), $tag));
@@ -120,4 +120,16 @@
       ->setBackground(PHUIObjectBoxView::BLUE_PROPERTY)
       ->addPropertyList($properties);
   }
+
+  private function buildPropertyValue($value) {
+    $viewer = $this->getViewer();
+
+    if ($value == DiffusionIdentityUnassignedDatasource::FUNCTION_TOKEN) {
+      return phutil_tag('em', array(), pht('Explicitly Unassigned'));
+    } else if (!$value) {
+      return null;
+    } else {
+      return $viewer->renderHandle($value);
+    }
+  }
 }
diff --git a/src/applications/diffusion/editfield/DiffusionIdentityAssigneeEditField.php b/src/applications/diffusion/editfield/DiffusionIdentityAssigneeEditField.php
new file mode 100644
--- /dev/null
+++ b/src/applications/diffusion/editfield/DiffusionIdentityAssigneeEditField.php
@@ -0,0 +1,22 @@
+<?php
+
+final class DiffusionIdentityAssigneeEditField
+  extends PhabricatorTokenizerEditField {
+
+  protected function newDatasource() {
+    return new DiffusionIdentityAssigneeDatasource();
+  }
+
+  protected function newHTTPParameterType() {
+    return new AphrontUserListHTTPParameterType();
+  }
+
+  protected function newConduitParameterType() {
+    if ($this->getIsSingleValue()) {
+      return new ConduitUserParameterType();
+    } else {
+      return new ConduitUserListParameterType();
+    }
+  }
+
+}
diff --git a/src/applications/diffusion/query/DiffusionRepositoryIdentitySearchEngine.php b/src/applications/diffusion/query/DiffusionRepositoryIdentitySearchEngine.php
--- a/src/applications/diffusion/query/DiffusionRepositoryIdentitySearchEngine.php
+++ b/src/applications/diffusion/query/DiffusionRepositoryIdentitySearchEngine.php
@@ -17,6 +17,14 @@
 
   protected function buildCustomSearchFields() {
     return array(
+      id(new DiffusionIdentityAssigneeSearchField())
+        ->setLabel(pht('Assigned To'))
+        ->setKey('assignee')
+        ->setDescription(pht('Search for identities by assignee.')),
+      id(new PhabricatorSearchTextField())
+        ->setLabel(pht('Identity Contains'))
+        ->setKey('match')
+        ->setDescription(pht('Search for identities by substring.')),
       id(new PhabricatorSearchThreeStateField())
         ->setLabel(pht('Is Assigned'))
         ->setKey('hasEffectivePHID')
@@ -34,6 +42,14 @@
       $query->withHasEffectivePHID($map['hasEffectivePHID']);
     }
 
+    if ($map['match'] !== null) {
+      $query->withIdentityNameLike($map['match']);
+    }
+
+    if ($map['assignee']) {
+      $query->withAssigneePHIDs($map['assignee']);
+    }
+
     return $query;
   }
 
diff --git a/src/applications/diffusion/searchfield/DiffusionIdentityAssigneeSearchField.php b/src/applications/diffusion/searchfield/DiffusionIdentityAssigneeSearchField.php
new file mode 100644
--- /dev/null
+++ b/src/applications/diffusion/searchfield/DiffusionIdentityAssigneeSearchField.php
@@ -0,0 +1,22 @@
+<?php
+
+final class DiffusionIdentityAssigneeSearchField
+  extends PhabricatorSearchTokenizerField {
+
+  protected function getDefaultValue() {
+    return array();
+  }
+
+  protected function getValueFromRequest(AphrontRequest $request, $key) {
+    return $this->getUsersFromRequest($request, $key);
+  }
+
+  protected function newDatasource() {
+    return new DiffusionIdentityAssigneeDatasource();
+  }
+
+  protected function newConduitParameterType() {
+    return new ConduitUserListParameterType();
+  }
+
+}
diff --git a/src/applications/diffusion/typeahead/DiffusionIdentityAssigneeDatasource.php b/src/applications/diffusion/typeahead/DiffusionIdentityAssigneeDatasource.php
new file mode 100644
--- /dev/null
+++ b/src/applications/diffusion/typeahead/DiffusionIdentityAssigneeDatasource.php
@@ -0,0 +1,21 @@
+<?php
+
+final class DiffusionIdentityAssigneeDatasource
+  extends PhabricatorTypeaheadCompositeDatasource {
+
+  public function getBrowseTitle() {
+    return pht('Browse Assignee');
+  }
+
+  public function getPlaceholderText() {
+    return pht('Type a username or function...');
+  }
+
+  public function getComponentDatasources() {
+    return array(
+      new PhabricatorPeopleDatasource(),
+      new DiffusionIdentityUnassignedDatasource(),
+    );
+  }
+
+}
diff --git a/src/applications/diffusion/typeahead/DiffusionIdentityUnassignedDatasource.php b/src/applications/diffusion/typeahead/DiffusionIdentityUnassignedDatasource.php
new file mode 100644
--- /dev/null
+++ b/src/applications/diffusion/typeahead/DiffusionIdentityUnassignedDatasource.php
@@ -0,0 +1,77 @@
+<?php
+
+final class DiffusionIdentityUnassignedDatasource
+  extends PhabricatorTypeaheadDatasource {
+
+  const FUNCTION_TOKEN = 'unassigned()';
+
+  public function getBrowseTitle() {
+    return pht('Browse Explicitly Unassigned');
+  }
+
+  public function getPlaceholderText() {
+    return pht('Type "unassigned"...');
+  }
+
+  public function getDatasourceApplicationClass() {
+    return 'PhabricatorDiffusionApplication';
+  }
+
+  public function getDatasourceFunctions() {
+    return array(
+      'unassigned' => array(
+        'name' => pht('Explicitly Unassigned'),
+        'summary' => pht('Find results which are not assigned.'),
+        'description' => pht(
+          "This function includes results which have been explicitly ".
+          "unassigned. Use a query like this to find explicitly ".
+          "unassigned results:\n\n%s\n\n".
+          "If you combine this function with other functions, the query will ".
+          "return results which match the other selectors //or// have no ".
+          "assignee. For example, this query will find results which are ".
+          "assigned to `alincoln`, and will also find results which have been ".
+          "unassigned:\n\n%s",
+          '> unassigned()',
+          '> alincoln, unassigned()'),
+      ),
+    );
+  }
+
+  public function loadResults() {
+    $results = array(
+      $this->buildUnassignedResult(),
+    );
+    return $this->filterResultsAgainstTokens($results);
+  }
+
+  protected function evaluateFunction($function, array $argv_list) {
+    $results = array();
+
+    foreach ($argv_list as $argv) {
+      $results[] = self::FUNCTION_TOKEN;
+    }
+
+    return $results;
+  }
+
+  public function renderFunctionTokens($function, array $argv_list) {
+    $results = array();
+    foreach ($argv_list as $argv) {
+      $results[] = PhabricatorTypeaheadTokenView::newFromTypeaheadResult(
+        $this->buildUnassignedResult());
+    }
+    return $results;
+  }
+
+  private function buildUnassignedResult() {
+    $name = pht('Unassigned');
+    return $this->newFunctionResult()
+      ->setName($name.' unassigned')
+      ->setDisplayName($name)
+      ->setIcon('fa-ban')
+      ->setPHID('unassigned()')
+      ->setUnique(true)
+      ->addAttribute(pht('Select results with no owner.'));
+  }
+
+}
diff --git a/src/applications/people/editor/PhabricatorUserEditor.php b/src/applications/people/editor/PhabricatorUserEditor.php
--- a/src/applications/people/editor/PhabricatorUserEditor.php
+++ b/src/applications/people/editor/PhabricatorUserEditor.php
@@ -420,6 +420,12 @@
       $user->endWriteLocking();
     $user->saveTransaction();
 
+    // Try and match this new address against unclaimed `RepositoryIdentity`s
+    PhabricatorWorker::scheduleTask(
+      'PhabricatorRepositoryIdentityChangeWorker',
+      array('userPHID' => $user->getPHID()),
+      array('objectPHID' => $user->getPHID()));
+
     return $this;
   }
 
diff --git a/src/applications/repository/engine/PhabricatorRepositoryIdentityEditEngine.php b/src/applications/repository/engine/PhabricatorRepositoryIdentityEditEngine.php
--- a/src/applications/repository/engine/PhabricatorRepositoryIdentityEditEngine.php
+++ b/src/applications/repository/engine/PhabricatorRepositoryIdentityEditEngine.php
@@ -75,7 +75,7 @@
 
   protected function buildCustomEditFields($object) {
     return array(
-      id(new PhabricatorUsersEditField())
+      id(new DiffusionIdentityAssigneeEditField())
         ->setKey('manuallySetUserPHID')
         ->setLabel(pht('Assigned To'))
         ->setDescription(pht('Override this identity\'s assignment.'))
diff --git a/src/applications/repository/query/PhabricatorRepositoryIdentityQuery.php b/src/applications/repository/query/PhabricatorRepositoryIdentityQuery.php
--- a/src/applications/repository/query/PhabricatorRepositoryIdentityQuery.php
+++ b/src/applications/repository/query/PhabricatorRepositoryIdentityQuery.php
@@ -6,6 +6,9 @@
   private $ids;
   private $phids;
   private $identityNames;
+  private $emailAddress;
+  private $assigneePHIDs;
+  private $identityNameLike;
   private $hasEffectivePHID;
 
   public function withIDs(array $ids) {
@@ -23,6 +26,21 @@
     return $this;
   }
 
+  public function withIdentityNameLike($name_like) {
+    $this->identityNameLike = $name_like;
+    return $this;
+  }
+
+  public function withEmailAddress($address) {
+    $this->emailAddress = $address;
+    return $this;
+  }
+
+  public function withAssigneePHIDs(array $assignees) {
+    $this->assigneePHIDs = $assignees;
+    return $this;
+  }
+
   public function withHasEffectivePHID($has_effective_phid) {
     $this->hasEffectivePHID = $has_effective_phid;
     return $this;
@@ -57,8 +75,14 @@
         $this->phids);
     }
 
-    if ($this->hasEffectivePHID !== null) {
+    if ($this->assigneePHIDs !== null) {
+      $where[] = qsprintf(
+        $conn,
+        'repository_identity.currentEffectiveUserPHID IN (%Ls)',
+        $this->assigneePHIDs);
+    }
 
+    if ($this->hasEffectivePHID !== null) {
       if ($this->hasEffectivePHID) {
         $where[] = qsprintf(
           $conn,
@@ -82,6 +106,21 @@
         $name_hashes);
     }
 
+    if ($this->emailAddress !== null) {
+      $identity_style = "<{$this->emailAddress}>";
+      $where[] = qsprintf(
+        $conn,
+        'repository_identity.identityNameRaw LIKE %<',
+        $identity_style);
+    }
+
+    if ($this->identityNameLike != null) {
+      $where[] = qsprintf(
+        $conn,
+        'repository_identity.identityNameRaw LIKE %~',
+        $this->identityNameLike);
+    }
+
     return $where;
   }
 
diff --git a/src/applications/repository/storage/PhabricatorRepositoryCommit.php b/src/applications/repository/storage/PhabricatorRepositoryCommit.php
--- a/src/applications/repository/storage/PhabricatorRepositoryCommit.php
+++ b/src/applications/repository/storage/PhabricatorRepositoryCommit.php
@@ -21,6 +21,8 @@
 
   protected $repositoryID;
   protected $phid;
+  protected $authorIdentityPHID;
+  protected $committerIdentityPHID;
   protected $commitIdentifier;
   protected $epoch;
   protected $mailKey;
@@ -113,6 +115,8 @@
         'commitIdentifier' => 'text40',
         'mailKey' => 'bytes20',
         'authorPHID' => 'phid?',
+        'authorIdentityPHID' => 'phid?',
+        'committerIdentityPHID' => 'phid?',
         'auditStatus' => 'uint32',
         'summary' => 'text255',
         'importStatus' => 'uint32',
diff --git a/src/applications/repository/storage/PhabricatorRepositoryIdentity.php b/src/applications/repository/storage/PhabricatorRepositoryIdentity.php
--- a/src/applications/repository/storage/PhabricatorRepositoryIdentity.php
+++ b/src/applications/repository/storage/PhabricatorRepositoryIdentity.php
@@ -80,6 +80,7 @@
   public function getCapabilities() {
     return array(
       PhabricatorPolicyCapability::CAN_VIEW,
+      PhabricatorPolicyCapability::CAN_EDIT,
     );
   }
 
diff --git a/src/applications/repository/worker/PhabricatorRepositoryIdentityChangeWorker.php b/src/applications/repository/worker/PhabricatorRepositoryIdentityChangeWorker.php
new file mode 100644
--- /dev/null
+++ b/src/applications/repository/worker/PhabricatorRepositoryIdentityChangeWorker.php
@@ -0,0 +1,34 @@
+<?php
+
+final class PhabricatorRepositoryIdentityChangeWorker
+extends PhabricatorWorker {
+
+  protected function doWork() {
+    $viewer = PhabricatorUser::getOmnipotentUser();
+
+    $task_data = $this->getTaskData();
+    $user_phid = idx($task_data, 'userPHID');
+
+    $user = id(new PhabricatorPeopleQuery())
+      ->withPHIDs(array($user_phid))
+      ->setViewer($viewer)
+      ->executeOne();
+
+    $emails = id(new PhabricatorUserEmail())->loadAllWhere(
+      'userPHID = %s ORDER BY address',
+      $user->getPHID());
+
+    foreach ($emails as $email) {
+      $identities = id(new PhabricatorRepositoryIdentityQuery())
+        ->setViewer($viewer)
+        ->withEmailAddress($email->getAddress())
+        ->execute();
+
+      foreach ($identities as $identity) {
+        $identity->setAutomaticGuessedUserPHID($user->getPHID())
+          ->save();
+      }
+    }
+  }
+
+}
diff --git a/src/applications/repository/worker/commitmessageparser/PhabricatorRepositoryCommitMessageParserWorker.php b/src/applications/repository/worker/commitmessageparser/PhabricatorRepositoryCommitMessageParserWorker.php
--- a/src/applications/repository/worker/commitmessageparser/PhabricatorRepositoryCommitMessageParserWorker.php
+++ b/src/applications/repository/worker/commitmessageparser/PhabricatorRepositoryCommitMessageParserWorker.php
@@ -109,6 +109,8 @@
     $data->setCommitDetail('authorName', $ref->getAuthorName());
     $data->setCommitDetail('authorEmail', $ref->getAuthorEmail());
 
+    $data->setCommitDetail(
+      'authorIdentityPHID', $author_identity->getPHID());
     $data->setCommitDetail(
       'authorPHID',
       $this->resolveUserPHID($commit, $author));
@@ -124,6 +126,8 @@
       $data->setCommitDetail(
         'committerPHID',
         $this->resolveUserPHID($commit, $committer));
+      $data->setCommitDetail(
+        'committerIdentityPHID', $committer_identity->getPHID());
     }
 
     $repository = $this->repository;
@@ -161,6 +165,9 @@
       $commit->setAuthorPHID($author_phid);
     }
 
+    $commit->setAuthorIdentityPHID($author_identity->getPHID());
+    $commit->setCommitterIdentityPHID($committer_identity->getPHID());
+
     $commit->setSummary($data->getSummary());
     $commit->save();
 
diff --git a/src/applications/repository/xaction/PhabricatorRepositoryIdentityAssignTransaction.php b/src/applications/repository/xaction/PhabricatorRepositoryIdentityAssignTransaction.php
--- a/src/applications/repository/xaction/PhabricatorRepositoryIdentityAssignTransaction.php
+++ b/src/applications/repository/xaction/PhabricatorRepositoryIdentityAssignTransaction.php
@@ -21,23 +21,33 @@
       return pht(
         '%s assigned this identity to %s.',
         $this->renderAuthor(),
-        $this->renderHandle($new));
+        $this->renderIdentityHandle($new));
     } else if (!$new) {
       return pht(
         '%s removed %s as the assignee of this identity.',
         $this->renderAuthor(),
-        $this->renderHandle($old));
+        $this->renderIdentityHandle($old));
     } else {
       return pht(
         '%s changed the assigned user for this identity from %s to %s.',
         $this->renderAuthor(),
-        $this->renderHandle($old),
-        $this->renderHandle($new));
+        $this->renderIdentityHandle($old),
+        $this->renderIdentityHandle($new));
+    }
+  }
+
+  private function renderIdentityHandle($handle) {
+    $unassigned_token = DiffusionIdentityUnassignedDatasource::FUNCTION_TOKEN;
+    if ($handle === $unassigned_token) {
+      return phutil_tag('em', array(), pht('Explicitly Unassigned'));
+    } else {
+      return $this->renderHandle($handle);
     }
   }
 
   public function validateTransactions($object, array $xactions) {
     $errors = array();
+    $unassigned_token = DiffusionIdentityUnassignedDatasource::FUNCTION_TOKEN;
 
     foreach ($xactions as $xaction) {
       $old = $xaction->getOldValue();
@@ -50,6 +60,10 @@
         continue;
       }
 
+      if ($new === $unassigned_token) {
+        continue;
+      }
+
       $assignee_list = id(new PhabricatorPeopleQuery())
         ->setViewer($this->getActor())
         ->withPHIDs(array($new))