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
@@ -600,6 +600,7 @@
     'DiffusionCommitRevisionReviewersHeraldField' => 'applications/diffusion/herald/DiffusionCommitRevisionReviewersHeraldField.php',
     'DiffusionCommitRevisionSubscribersHeraldField' => 'applications/diffusion/herald/DiffusionCommitRevisionSubscribersHeraldField.php',
     'DiffusionCommitTagsController' => 'applications/diffusion/controller/DiffusionCommitTagsController.php',
+    'DiffusionCompareController' => 'applications/diffusion/controller/DiffusionCompareController.php',
     'DiffusionConduitAPIMethod' => 'applications/diffusion/conduit/DiffusionConduitAPIMethod.php',
     'DiffusionController' => 'applications/diffusion/controller/DiffusionController.php',
     'DiffusionCreateCommentConduitAPIMethod' => 'applications/diffusion/conduit/DiffusionCreateCommentConduitAPIMethod.php',
@@ -757,6 +758,7 @@
     'DiffusionRequest' => 'applications/diffusion/request/DiffusionRequest.php',
     'DiffusionResolveRefsConduitAPIMethod' => 'applications/diffusion/conduit/DiffusionResolveRefsConduitAPIMethod.php',
     'DiffusionResolveUserQuery' => 'applications/diffusion/query/DiffusionResolveUserQuery.php',
+    'DiffusionRevlistConduitAPIMethod' => 'applications/diffusion/conduit/DiffusionRevlistConduitAPIMethod.php',
     'DiffusionSSHWorkflow' => 'applications/diffusion/ssh/DiffusionSSHWorkflow.php',
     'DiffusionSearchQueryConduitAPIMethod' => 'applications/diffusion/conduit/DiffusionSearchQueryConduitAPIMethod.php',
     'DiffusionServeController' => 'applications/diffusion/controller/DiffusionServeController.php',
@@ -4675,6 +4677,7 @@
     'DiffusionCommitRevisionReviewersHeraldField' => 'DiffusionCommitHeraldField',
     'DiffusionCommitRevisionSubscribersHeraldField' => 'DiffusionCommitHeraldField',
     'DiffusionCommitTagsController' => 'DiffusionController',
+    'DiffusionCompareController' => 'DiffusionController',
     'DiffusionConduitAPIMethod' => 'ConduitAPIMethod',
     'DiffusionController' => 'PhabricatorController',
     'DiffusionCreateCommentConduitAPIMethod' => 'DiffusionConduitAPIMethod',
@@ -4832,6 +4835,7 @@
     'DiffusionRequest' => 'Phobject',
     'DiffusionResolveRefsConduitAPIMethod' => 'DiffusionQueryConduitAPIMethod',
     'DiffusionResolveUserQuery' => 'Phobject',
+    'DiffusionRevlistConduitAPIMethod' => 'DiffusionQueryConduitAPIMethod',
     'DiffusionSSHWorkflow' => 'PhabricatorSSHWorkflow',
     'DiffusionSearchQueryConduitAPIMethod' => 'DiffusionQueryConduitAPIMethod',
     'DiffusionServeController' => 'DiffusionController',
diff --git a/src/applications/diffusion/application/PhabricatorDiffusionApplication.php b/src/applications/diffusion/application/PhabricatorDiffusionApplication.php
--- a/src/applications/diffusion/application/PhabricatorDiffusionApplication.php
+++ b/src/applications/diffusion/application/PhabricatorDiffusionApplication.php
@@ -77,6 +77,7 @@
           'browse/(?P<dblob>.*)'        => 'DiffusionBrowseController',
           'lastmodified/(?P<dblob>.*)'  => 'DiffusionLastModifiedController',
           'diff/'                       => 'DiffusionDiffController',
+          'compare/'                    => 'DiffusionCompareController',
           'tags/(?P<dblob>.*)'          => 'DiffusionTagListController',
           'branches/(?P<dblob>.*)'      => 'DiffusionBranchTableController',
           'refs/(?P<dblob>.*)'          => 'DiffusionRefTableController',
diff --git a/src/applications/diffusion/conduit/DiffusionRevlistConduitAPIMethod.php b/src/applications/diffusion/conduit/DiffusionRevlistConduitAPIMethod.php
new file mode 100644
--- /dev/null
+++ b/src/applications/diffusion/conduit/DiffusionRevlistConduitAPIMethod.php
@@ -0,0 +1,115 @@
+<?php
+
+final class DiffusionRevlistConduitAPIMethod
+  extends DiffusionQueryConduitAPIMethod {
+
+  private $parents = array();
+  private $cherryPicked = array();
+  private $mergeBase;
+  private $listCount;
+  private $reverseListCount;
+
+  public function getAPIMethodName() {
+    return 'diffusion.revlist';
+  }
+
+  public function getMethodDescription() {
+    return pht('Returns list of commites between two branches.');
+  }
+
+  protected function defineReturnType() {
+    return 'array';
+  }
+
+  protected function defineCustomParamTypes() {
+    return array(
+      'from' => 'required string',
+      'onto' => 'required string',
+      'path' => 'optional string',
+      'offset' => 'required int',
+      'limit' => 'required int',
+    );
+  }
+
+  protected function getResult(ConduitAPIRequest $request) {
+    $path_changes = parent::getResult($request);
+
+    return array(
+      'pathChanges' => mpull($path_changes, 'toDictionary'),
+      'parents' => $this->parents,
+      'cherryPicked' => $this->cherryPicked,
+      'mergeBase' => $this->mergeBase,
+      'commitsCount' => $this->listCount,
+      'reversedComparisonSize' => $this->reverseListCount,
+    );
+  }
+
+  protected function getGitResult(ConduitAPIRequest $request) {
+    $drequest = $this->getDiffusionRequest();
+    $repository = $drequest->getRepository();
+    $from = $request->getValue('from');
+    $onto = $request->getValue('onto');
+    $path = $request->getValue('path', '');
+    $offset = $request->getValue('offset');
+    $limit = $request->getValue('limit');
+
+
+    list($stdout) = $repository->execxLocalCommand(
+      'rev-list '.
+        '--skip=%d '.
+        '-n %d '.
+        '--parents '.
+        '--left-only '.
+        '%s...%s -- %C',
+      $offset,
+      $limit,
+      $from,
+      $onto,
+      // Git omits merge commits if the path is provided, even if it is empty.
+      (strlen($path) ? csprintf('%s', $path) : ''));
+
+    $lines = explode("\n", trim($stdout));
+    $lines = array_filter($lines);
+    if (!$lines) {
+      return array();
+    }
+
+    $hash_list = array();
+    $parent_map = array();
+    $cherry_picked = array();
+    foreach ($lines as $line) {
+      list($hash, $parents) = explode(' ', $line, 2);
+      $hash_list[] = $hash;
+      $parent_map[$hash] = preg_split('/\s+/', $parents);
+    }
+
+    $this->parents = $parent_map;
+    $this->cherryPicked = $cherry_picked;
+
+     list($stdout) = $repository->execxLocalCommand(
+      'rev-list '.
+        '--count '.
+        '--left-right '.
+        '%s...%s -- %C',
+      $from,
+      $onto,
+      // Git omits merge commits if the path is provided, even if it is empty.
+      (strlen($path) ? csprintf('%s', $path) : ''));
+
+    list($count, $reverse_count) = preg_split('/\s+/', $stdout, 2);
+    $this->listCount = $count;
+    $this->reverseListCount = $reverse_count;
+
+    list($stdout) = $repository->execxLocalCommand(
+      'merge-base '.
+        '%s %s',
+      $from,
+      $onto);
+
+    $this->mergeBase = $stdout;
+
+    return DiffusionQuery::loadHistoryForCommitIdentifiers(
+      $hash_list,
+      $drequest);
+  }
+}
diff --git a/src/applications/diffusion/controller/DiffusionCompareController.php b/src/applications/diffusion/controller/DiffusionCompareController.php
new file mode 100644
--- /dev/null
+++ b/src/applications/diffusion/controller/DiffusionCompareController.php
@@ -0,0 +1,251 @@
+<?php
+
+final class DiffusionCompareController extends DiffusionController {
+
+  public function shouldAllowPublic() {
+    return true;
+  }
+
+  public function handleRequest(AphrontRequest $request) {
+    $response = $this->loadDiffusionContext();
+    if ($response) {
+      return $response;
+    }
+
+    $viewer = $this->getViewer();
+    $drequest = $this->getDiffusionRequest();
+    $repository = $drequest->getRepository();
+
+    $content = array();
+
+    $crumbs = $this->buildCrumbs(array('view' => 'compare'));
+
+    $empty_title = null;
+    $error_message = null;
+
+    if ($repository->getVersionControlSystem() !=
+          PhabricatorRepositoryType::REPOSITORY_TYPE_GIT) {
+      $empty_title = pht('Not supported');
+      $error_message = pht(
+        'This feature is not yet supported for %s repositories.',
+        $repository->getVersionControlSystem());
+      $content[] = id(new PHUIInfoView())
+        ->setTitle($empty_title)
+        ->setSeverity(PHUIInfoView::SEVERITY_WARNING)
+        ->setErrors(array($error_message));
+    }
+
+    $from_ref = $request->getStr('from');
+    $onto_ref = $request->getStr('onto');
+
+    $refs = id(new DiffusionCachedResolveRefsQuery())
+      ->setRepository($repository)
+      ->withRefs(array($from_ref, $onto_ref))
+      ->execute();
+
+
+    if (count($refs) == 2) {
+      $content[] = $this->buildCompareContent($drequest);
+    } else {
+      $content[] = $this->buildCompareForm($request, $refs);
+    }
+
+
+    return $this->newPage()
+      ->setTitle(
+        array(
+          $repository->getName(),
+          $repository->getDisplayName(),
+        ))
+      ->setCrumbs($crumbs)
+      ->appendChild($content);
+  }
+
+  private function buildCompareForm(AphrontRequest $request, array $resolved) {
+    $viewer = $this->getViewer();
+
+    $from_ref = $request->getStr('from');
+    $onto_ref = $request->getStr('onto');
+
+    if (idx($resolved, $from_ref)) {
+      $e_from = null;
+    } else {
+      $e_from = 'Not Found';
+    }
+
+    if (idx($resolved, $onto_ref)) {
+      $e_onto = null;
+    } else {
+      $e_onto = 'Not Found';
+    }
+
+
+    $form = id(new AphrontFormView())
+      ->setUser($viewer)
+      ->setMethod('GET')
+      ->appendControl(
+        id(new AphrontFormTextControl())
+          ->setLabel(pht('From'))
+          ->setName('from')
+          ->setError($e_from)
+          ->setValue($from_ref))
+      ->appendControl(
+        id(new AphrontFormTextControl())
+          ->setLabel(pht('Onto'))
+          ->setName('onto')
+          ->setError($e_onto)
+          ->setValue($onto_ref))
+      ->appendControl(
+        id(new AphrontFormSubmitControl())
+          ->setValue('Compare'));
+
+    return $form;
+  }
+
+  private function buildCompareContent(DiffusionRequest $drequest) {
+    $request = $this->getRequest();
+    $repository = $drequest->getRepository();
+
+    $from_ref = $request->getStr('from');
+    $onto_ref = $request->getStr('onto');
+
+    $content = array();
+
+    try {
+      $revlist = $this->callConduitWithDiffusionRequest(
+        'diffusion.revlist',
+        array(
+          'from' => $from_ref,
+          'onto' => $onto_ref,
+          'path' => $drequest->getPath(),
+          'offset' => 0,
+          'limit' => 100,
+        ));
+      $history = DiffusionPathChange::newFromConduit(
+        $revlist['pathChanges']);
+
+      $history_exception = null;
+    } catch (Exception $ex) {
+      $revlist = null;
+      $history = null;
+      $history_exception = $ex;
+    }
+
+
+    $content[] = $this->buildCompareProperties($drequest, $revlist);
+    $content[] = $this->buildCompareForm(
+      $request,
+      array($from_ref => true, $onto_ref => true));
+
+    $content[] = $this->buildHistoryTable(
+      $revlist,
+      $history,
+      $history_exception);
+
+    return $content;
+  }
+
+  private function buildCompareProperties($drequest, $revlist) {
+    $viewer = $this->getViewer();
+
+    $request = $this->getRequest();
+    $repository = $drequest->getRepository();
+
+    $from_ref = $request->getStr('from');
+    $onto_ref = $request->getStr('onto');
+
+    $reverse_uri = $repository->getPathURI(
+      "compare/?from=${onto_ref}&onto=${from_ref}");
+    $actions = id(new PhabricatorActionListView());
+    $actions->setUser($viewer);
+
+
+    $actions->addAction(id(new PhabricatorActionView())
+        ->setName(pht('Reverse Comparison'))
+        ->setHref($reverse_uri)
+        ->setIcon('fa-list'));
+
+    $view = id(new PHUIPropertyListView())
+      ->setUser($viewer)
+      ->setActionList($actions);
+
+    $readme =
+      'These are the commits that will be added to **Onto** if you merge '.
+      '**From** onto it.';
+    $readme = new PHUIRemarkupView($viewer, $readme);
+    $view->addTextContent($readme);
+
+    $view->addProperty(pht('From'), $from_ref);
+    $view->addProperty(pht('Onto'), $onto_ref);
+    $view->addProperty(
+      pht('merge-base'),
+      new PHUIRemarkupView($viewer, idx($revlist, 'mergeBase')));
+
+    $compare_text = pht(
+      '%d Commits (Reverse comparison is %d commits)',
+      idx($revlist, 'commitsCount'),
+      idx($revlist, 'reversedComparisonSize'));
+    $view->addProperty(pht('Comparison size'), $compare_text);
+
+    $merge_instructions = "`git checkout ${onto_ref} && git merge ${from_ref}`";
+    $merge_instructions = new PHUIRemarkupView($viewer, $merge_instructions);
+    $view->addProperty(pht('To Merge'), $merge_instructions);
+
+    $header = id(new PHUIHeaderView())
+      ->setUser($viewer)
+      ->setPolicyObject($drequest->getRepository());
+
+    $box = id(new PHUIObjectBoxView())
+      ->setUser($viewer)
+      ->setHeader($header)
+      ->addPropertyList($view);
+    return $box;
+  }
+
+  private function buildHistoryTable(
+    $revlist,
+    $history,
+    $history_exception) {
+
+    $request = $this->getRequest();
+    $viewer = $request->getUser();
+    $drequest = $this->getDiffusionRequest();
+    $repository = $drequest->getRepository();
+
+    if ($history_exception) {
+      if ($repository->isImporting()) {
+        return $this->renderStatusMessage(
+          pht('Still Importing...'),
+          pht(
+            'This repository is still importing. History is not yet '.
+            'available.'));
+      } else {
+        return $this->renderStatusMessage(
+          pht('Unable to Retrieve History'),
+          $history_exception->getMessage());
+      }
+    }
+
+    $history_table = id(new DiffusionHistoryTableView())
+      ->setUser($viewer)
+      ->setDiffusionRequest($drequest)
+      ->setHistory($history);
+
+    // TODO: Super sketchy?
+    $history_table->loadRevisions();
+
+    if ($revlist) {
+      $history_table->setParents($revlist['parents']);
+    }
+
+    // TODO also expose diff.
+
+    $panel = new PHUIObjectBoxView();
+    $header = id(new PHUIHeaderView())
+      ->setHeader(pht('Missing Commits'));
+    $panel->setHeader($header);
+    $panel->setTable($history_table);
+
+    return $panel;
+  }
+}
diff --git a/src/applications/diffusion/controller/DiffusionController.php b/src/applications/diffusion/controller/DiffusionController.php
--- a/src/applications/diffusion/controller/DiffusionController.php
+++ b/src/applications/diffusion/controller/DiffusionController.php
@@ -206,6 +206,9 @@
       case 'change':
         $view_name = pht('Change');
         break;
+      case 'compare':
+        $view_name = pht('Compare');
+        break;
     }
 
     $crumb = id(new PHUICrumbView())
diff --git a/src/applications/diffusion/controller/DiffusionRepositoryController.php b/src/applications/diffusion/controller/DiffusionRepositoryController.php
--- a/src/applications/diffusion/controller/DiffusionRepositoryController.php
+++ b/src/applications/diffusion/controller/DiffusionRepositoryController.php
@@ -506,6 +506,12 @@
           ->setHref($push_uri));
     }
 
+    $view->addAction(
+      id(new PhabricatorActionView())
+        ->setName(pht('Compare Branches'))
+        ->setIcon('fa-usb')
+        ->setHref($repository->getPathURI('compare/')));
+
     return $view;
   }