diff --git a/src/applications/diffusion/controller/DiffusionBrowseController.php b/src/applications/diffusion/controller/DiffusionBrowseController.php
index d720ad8872..be2df62dad 100644
--- a/src/applications/diffusion/controller/DiffusionBrowseController.php
+++ b/src/applications/diffusion/controller/DiffusionBrowseController.php
@@ -1,123 +1,296 @@
 <?php
 
 final class DiffusionBrowseController extends DiffusionController {
 
   public function processRequest() {
     $drequest = $this->diffusionRequest;
+    $is_file = false;
 
     if ($this->getRequest()->getStr('before')) {
-      $results = array();
       $is_file = true;
-    } else {
+    } else if ($this->getRequest()->getStr('grep') == '') {
       $browse_query = DiffusionBrowseQuery::newFromDiffusionRequest($drequest);
       $browse_query->setViewer($this->getRequest()->getUser());
       $results = $browse_query->loadPaths();
       $reason = $browse_query->getReasonForEmptyResultSet();
       $is_file = ($reason == DiffusionBrowseQuery::REASON_IS_FILE);
     }
 
+    if ($is_file) {
+      $controller = new DiffusionBrowseFileController($this->getRequest());
+      $controller->setDiffusionRequest($drequest);
+      $controller->setCurrentApplication($this->getCurrentApplication());
+      return $this->delegateToController($controller);
+    }
+
     $content = array();
 
     if ($drequest->getTagContent()) {
       $title = 'Tag: '.$drequest->getSymbolicCommit();
 
       $tag_view = new AphrontPanelView();
       $tag_view->setHeader($title);
       $tag_view->appendChild(
         $this->markupText($drequest->getTagContent()));
 
       $content[] = $tag_view;
     }
 
-    if (!$results) {
+    $content[] = $this->renderSearchForm();
 
-      if ($is_file) {
-        $controller = new DiffusionBrowseFileController($this->getRequest());
-        $controller->setDiffusionRequest($drequest);
-        $controller->setCurrentApplication($this->getCurrentApplication());
-        return $this->delegateToController($controller);
-      }
-
-      $empty_result = new DiffusionEmptyResultView();
-      $empty_result->setDiffusionRequest($drequest);
-      $empty_result->setBrowseQuery($browse_query);
-      $empty_result->setView($this->getRequest()->getStr('view'));
-      $content[] = $empty_result;
+    if ($this->getRequest()->getStr('grep') != '') {
+      $content[] = $this->renderSearchResults();
 
     } else {
+      if (!$results) {
+        $empty_result = new DiffusionEmptyResultView();
+        $empty_result->setDiffusionRequest($drequest);
+        $empty_result->setBrowseQuery($browse_query);
+        $empty_result->setView($this->getRequest()->getStr('view'));
+        $content[] = $empty_result;
+
+      } else {
 
-      $phids = array();
-      foreach ($results as $result) {
-        $data = $result->getLastCommitData();
-        if ($data) {
-          if ($data->getCommitDetail('authorPHID')) {
-            $phids[$data->getCommitDetail('authorPHID')] = true;
+        $phids = array();
+        foreach ($results as $result) {
+          $data = $result->getLastCommitData();
+          if ($data) {
+            if ($data->getCommitDetail('authorPHID')) {
+              $phids[$data->getCommitDetail('authorPHID')] = true;
+            }
           }
         }
-      }
 
-      $phids = array_keys($phids);
-      $handles = $this->loadViewerHandles($phids);
+        $phids = array_keys($phids);
+        $handles = $this->loadViewerHandles($phids);
 
-      $browse_table = new DiffusionBrowseTableView();
-      $browse_table->setDiffusionRequest($drequest);
-      $browse_table->setHandles($handles);
-      $browse_table->setPaths($results);
-      $browse_table->setUser($this->getRequest()->getUser());
+        $browse_table = new DiffusionBrowseTableView();
+        $browse_table->setDiffusionRequest($drequest);
+        $browse_table->setHandles($handles);
+        $browse_table->setPaths($results);
+        $browse_table->setUser($this->getRequest()->getUser());
 
-      $browse_panel = new AphrontPanelView();
-      $browse_panel->appendChild($browse_table);
-      $browse_panel->setNoBackground();
+        $browse_panel = new AphrontPanelView();
+        $browse_panel->appendChild($browse_table);
+        $browse_panel->setNoBackground();
 
-      $content[] = $browse_panel;
-    }
+        $content[] = $browse_panel;
+      }
 
-    $content[] = $this->buildOpenRevisions();
+      $content[] = $this->buildOpenRevisions();
 
-    $readme_content = $browse_query->renderReadme($results);
-    if ($readme_content) {
-      $readme_panel = new AphrontPanelView();
-      $readme_panel->setHeader('README');
-      $readme_panel->appendChild($readme_content);
+      $readme_content = $browse_query->renderReadme($results);
+      if ($readme_content) {
+        $readme_panel = new AphrontPanelView();
+        $readme_panel->setHeader('README');
+        $readme_panel->appendChild($readme_content);
 
-      $content[] = $readme_panel;
+        $content[] = $readme_panel;
+      }
     }
 
-
     $nav = $this->buildSideNav('browse', false);
     $nav->appendChild($content);
 
     $crumbs = $this->buildCrumbs(
       array(
         'branch' => true,
         'path'   => true,
         'view'   => 'browse',
       ));
     $nav->setCrumbs($crumbs);
 
     return $this->buildApplicationPage(
       $nav,
       array(
         'title' => array(
           nonempty(basename($drequest->getPath()), '/'),
           $drequest->getRepository()->getCallsign().' Repository',
         ),
       ));
   }
 
+
+  private function renderSearchForm() {
+    $drequest = $this->getDiffusionRequest();
+    $form = id(new AphrontFormView())
+      ->setUser($this->getRequest()->getUser())
+      ->setMethod('GET');
+
+    switch ($drequest->getRepository()->getVersionControlSystem()) {
+      case PhabricatorRepositoryType::REPOSITORY_TYPE_SVN:
+        $form->appendChild(pht('Search is not available in Subversion.'));
+        break;
+
+      default:
+        $form
+          ->appendChild(
+            id(new AphrontFormTextControl())
+              ->setLabel(pht('Search Here'))
+              ->setName('grep')
+              ->setValue($this->getRequest()->getStr('grep'))
+              ->setCaption(pht('Regular expression')))
+          ->appendChild(
+            id(new AphrontFormSubmitControl())
+              ->setValue(pht('Grep')));
+        break;
+    }
+
+    return $form;
+  }
+
+  private function renderSearchResults() {
+    $drequest = $this->getDiffusionRequest();
+    $repository = $drequest->getRepository();
+    $results = array();
+    $no_data = pht('No results found.');
+
+    $limit = 100;
+    $page = $this->getRequest()->getInt('page', 0);
+    $pager = new AphrontPagerView();
+    $pager->setPageSize($limit);
+    $pager->setOffset($page);
+    $pager->setURI($this->getRequest()->getRequestURI(), 'page');
+
+    try {
+
+      switch ($repository->getVersionControlSystem()) {
+        case PhabricatorRepositoryType::REPOSITORY_TYPE_GIT:
+          $future = $repository->getLocalCommandFuture(
+            // NOTE: --perl-regexp is available only with libpcre compiled in.
+            'grep --extended-regexp --null -n --no-color -e %s %s -- %s',
+            $this->getRequest()->getStr('grep'),
+            $drequest->getStableCommitName(),
+            $drequest->getPath());
+
+          $binary_pattern = '/Binary file [^:]*:(.+) matches/';
+          $lines = new LinesOfALargeExecFuture($future);
+          foreach ($lines as $line) {
+            $result = null;
+            if (preg_match('/[^:]*:(.+)\0(.+)\0(.*)/', $line, $result)) {
+              $results[] = array_slice($result, 1);
+            } else if (preg_match($binary_pattern, $line, $result)) {
+              list(, $path) = $result;
+              $results[] = array($path, null, pht('Binary file'));
+            } else {
+              $results[] = array(null, null, $line);
+            }
+            if (count($results) > $page + $limit) {
+              break;
+            }
+          }
+          unset($lines);
+
+          break;
+
+        case PhabricatorRepositoryType::REPOSITORY_TYPE_MERCURIAL:
+          $future = $repository->getLocalCommandFuture(
+            'grep --rev %s --print0 --line-number %s %s',
+            hgsprintf('ancestors(%s)', $drequest->getStableCommitName()),
+            $this->getRequest()->getStr('grep'),
+            $drequest->getPath());
+
+          $lines = id(new LinesOfALargeExecFuture($future))->setDelimiter("\0");
+          $parts = array();
+          foreach ($lines as $line) {
+            $parts[] = $line;
+            if (count($parts) == 4) {
+              list($path, $offset, $line, $string) = $parts;
+              $results[] = array($path, $line, $string);
+              if (count($results) > $page + $limit) {
+                break;
+              }
+              $parts = array();
+            }
+          }
+          unset($lines);
+
+          break;
+      }
+
+    } catch (CommandException $ex) {
+      return id(new AphrontErrorView())
+        ->setTitle(pht('Search Error'))
+        ->appendChild($ex->getStderr());
+    }
+
+    $results = array_slice($results, $page);
+    $results = $pager->sliceResults($results);
+
+    require_celerity_resource('syntax-highlighting-css');
+
+    // NOTE: This can be wrong because we may find the string inside the
+    // comment. But it's correct in most cases and highlighting the whole file
+    // would be too expensive.
+    $futures = array();
+    $engine = PhabricatorSyntaxHighlighter::newEngine();
+    foreach ($results as $result) {
+      list($path, $line, $string) = $result;
+      $futures["{$path}:{$line}"] = $engine->getHighlightFuture(
+        $engine->getLanguageFromFilename($path),
+        ltrim($string));
+    }
+
+    try {
+      Futures($futures)->limit(8)->resolveAll();
+    } catch (PhutilSyntaxHighlighterException $ex) {
+    }
+
+    $rows = array();
+    foreach ($results as $result) {
+      list($path, $line, $string) = $result;
+
+      $href = $drequest->generateURI(array(
+        'action' => 'browse',
+        'path' => $path,
+        'line' => $line,
+      ));
+
+      try {
+        $string = $futures["{$path}:{$line}"]->resolve();
+      } catch (PhutilSyntaxHighlighterException $ex) {
+      }
+
+      $string = phutil_tag(
+        'pre',
+        array('class' => 'PhabricatorMonospaced'),
+        $string);
+
+      $path = Filesystem::readablePath($path, $drequest->getPath());
+
+      $rows[] = array(
+        phutil_tag('a', array('href' => $href), $path),
+        $line,
+        $string,
+      );
+    }
+
+    $table = id(new AphrontTableView($rows))
+      ->setClassName('remarkup-code')
+      ->setHeaders(array(pht('Path'), pht('Line'), pht('String')))
+      ->setColumnClasses(array('', 'n', 'wide'))
+      ->setNoDataString($no_data);
+
+    return id(new AphrontPanelView())
+      ->setHeader(pht('Search Results'))
+      ->appendChild($table)
+      ->appendChild($pager);
+  }
+
+
   private function markupText($text) {
     $engine = PhabricatorMarkupEngine::newDiffusionMarkupEngine();
     $engine->setConfig('viewer', $this->getRequest()->getUser());
     $text = $engine->markupText($text);
 
     $text = phutil_tag(
       'div',
       array(
         'class' => 'phabricator-remarkup',
       ),
       $text);
 
     return $text;
   }
 
 }
diff --git a/src/applications/diffusion/query/browse/DiffusionBrowseQuery.php b/src/applications/diffusion/query/browse/DiffusionBrowseQuery.php
index d2151dd183..a0711f9aa7 100644
--- a/src/applications/diffusion/query/browse/DiffusionBrowseQuery.php
+++ b/src/applications/diffusion/query/browse/DiffusionBrowseQuery.php
@@ -1,157 +1,158 @@
 <?php
 
 abstract class DiffusionBrowseQuery {
 
   private $request;
 
   protected $reason;
   protected $existedAtCommit;
   protected $deletedAtCommit;
   protected $validityOnly;
   private $viewer;
 
   public function setViewer(PhabricatorUser $viewer) {
     $this->viewer = $viewer;
     return $this;
   }
 
   public function getViewer() {
     return $this->viewer;
   }
 
   const REASON_IS_FILE              = 'is-file';
   const REASON_IS_DELETED           = 'is-deleted';
   const REASON_IS_NONEXISTENT       = 'nonexistent';
   const REASON_BAD_COMMIT           = 'bad-commit';
   const REASON_IS_EMPTY             = 'empty';
   const REASON_IS_UNTRACKED_PARENT  = 'untracked-parent';
 
   final private function __construct() {
     // <private>
   }
 
   final public static function newFromDiffusionRequest(
     DiffusionRequest $request) {
 
     $repository = $request->getRepository();
 
     switch ($repository->getVersionControlSystem()) {
       case PhabricatorRepositoryType::REPOSITORY_TYPE_GIT:
         // TODO: Verify local-path?
         $query = new DiffusionGitBrowseQuery();
         break;
       case PhabricatorRepositoryType::REPOSITORY_TYPE_MERCURIAL:
         $query = new DiffusionMercurialBrowseQuery();
         break;
       case PhabricatorRepositoryType::REPOSITORY_TYPE_SVN:
         $query = new DiffusionSvnBrowseQuery();
         break;
       default:
         throw new Exception("Unsupported VCS!");
     }
 
     $query->request = $request;
 
     return $query;
   }
 
   final protected function getRequest() {
     return $this->request;
   }
 
   final public function getReasonForEmptyResultSet() {
     return $this->reason;
   }
 
   final public function getExistedAtCommit() {
     return $this->existedAtCommit;
   }
 
   final public function getDeletedAtCommit() {
     return $this->deletedAtCommit;
   }
 
   final public function loadPaths() {
+    $this->reason = null;
     return $this->executeQuery();
   }
 
   final public function shouldOnlyTestValidity() {
     return $this->validityOnly;
   }
 
   final public function needValidityOnly($need_validity_only) {
     $this->validityOnly = $need_validity_only;
     return $this;
   }
 
   final public function renderReadme(array $results) {
     $drequest = $this->getRequest();
 
     $readme = null;
     foreach ($results as $result) {
       $file_type = $result->getFileType();
       if (($file_type != ArcanistDiffChangeType::FILE_NORMAL) &&
           ($file_type != ArcanistDiffChangeType::FILE_TEXT)) {
         // Skip directories, etc.
         continue;
       }
 
       $path = $result->getPath();
 
       if (preg_match('/^readme(|\.txt|\.remarkup|\.rainbow)$/i', $path)) {
         $readme = $result;
         break;
       }
     }
 
     if (!$readme) {
       return null;
     }
 
     $readme_request = DiffusionRequest::newFromDictionary(
       array(
         'repository'  => $drequest->getRepository(),
         'commit'      => $drequest->getStableCommitName(),
         'path'        => $readme->getFullPath(),
       ));
 
     $content_query = DiffusionFileContentQuery::newFromDiffusionRequest(
       $readme_request);
     $content_query->setViewer($this->getViewer());
     $content_query->loadFileContent();
     $readme_content = $content_query->getRawData();
 
     if (preg_match('/\\.txt$/', $readme->getPath())) {
       $readme_content = phutil_escape_html_newlines($readme_content);
 
       $class = null;
     } else if (preg_match('/\\.rainbow$/', $readme->getPath())) {
       $highlighter = new PhutilRainbowSyntaxHighlighter();
       $readme_content = $highlighter
         ->getHighlightFuture($readme_content)
         ->resolve();
       $readme_content = phutil_escape_html_newlines($readme_content);
 
       require_celerity_resource('syntax-highlighting-css');
       $class = 'remarkup-code';
     } else {
       // Markup extensionless files as remarkup so we get links and such.
       $engine = PhabricatorMarkupEngine::newDiffusionMarkupEngine();
       $engine->setConfig('viewer', $this->getViewer());
       $readme_content = $engine->markupText($readme_content);
 
       $class = 'phabricator-remarkup';
     }
 
     $readme_content = phutil_tag(
       'div',
       array(
         'class' => $class,
       ),
       $readme_content);
 
     return $readme_content;
   }
 
   abstract protected function executeQuery();
 }