Index: src/__phutil_library_map__.php
===================================================================
--- src/__phutil_library_map__.php
+++ src/__phutil_library_map__.php
@@ -367,6 +367,7 @@
     'DifferentialFieldValidationException' => 'applications/differential/field/exception/DifferentialFieldValidationException.php',
     'DifferentialFreeformFieldSpecification' => 'applications/differential/field/specification/DifferentialFreeformFieldSpecification.php',
     'DifferentialFreeformFieldTestCase' => 'applications/differential/field/specification/__tests__/DifferentialFreeformFieldTestCase.php',
+    'DifferentialGetWorkingCopy' => 'applications/differential/DifferentialGetWorkingCopy.php',
     'DifferentialGitSVNIDFieldSpecification' => 'applications/differential/field/specification/DifferentialGitSVNIDFieldSpecification.php',
     'DifferentialHostFieldSpecification' => 'applications/differential/field/specification/DifferentialHostFieldSpecification.php',
     'DifferentialHovercardEventListener' => 'applications/differential/event/DifferentialHovercardEventListener.php',
@@ -418,6 +419,7 @@
     'DifferentialRevisionEditor' => 'applications/differential/editor/DifferentialRevisionEditor.php',
     'DifferentialRevisionIDFieldParserTestCase' => 'applications/differential/field/specification/__tests__/DifferentialRevisionIDFieldParserTestCase.php',
     'DifferentialRevisionIDFieldSpecification' => 'applications/differential/field/specification/DifferentialRevisionIDFieldSpecification.php',
+    'DifferentialRevisionLandController' => 'applications/differential/controller/DifferentialRevisionLandController.php',
     'DifferentialRevisionListController' => 'applications/differential/controller/DifferentialRevisionListController.php',
     'DifferentialRevisionListView' => 'applications/differential/view/DifferentialRevisionListView.php',
     'DifferentialRevisionMailReceiver' => 'applications/differential/mail/DifferentialRevisionMailReceiver.php',
@@ -2625,6 +2627,7 @@
     'DifferentialRevisionEditor' => 'PhabricatorEditor',
     'DifferentialRevisionIDFieldParserTestCase' => 'PhabricatorTestCase',
     'DifferentialRevisionIDFieldSpecification' => 'DifferentialFieldSpecification',
+    'DifferentialRevisionLandController' => 'DifferentialController',
     'DifferentialRevisionListController' =>
     array(
       0 => 'DifferentialController',
Index: src/applications/differential/DifferentialGetWorkingCopy.php
===================================================================
--- /dev/null
+++ src/applications/differential/DifferentialGetWorkingCopy.php
@@ -0,0 +1,54 @@
+<?php
+
+/**
+ * Can't find a good place for this, so I'm putting it in the most notably
+ * wrong place.
+ */
+final class DifferentialGetWorkingCopy {
+
+  /**
+   * Creates and/or cleans a workspace for the requested repo.
+   * tries to handle locking.
+   *
+   * return ArcanistGitAPI    TODO is this the right abstraction for server side?
+   */
+  public static function getCleanGitWorkspace(
+    PhabricatorRepository $repo) {
+
+    $origin_path = $repo->getLocalPath();
+
+    $path = rtrim($origin_path, '/');
+    $path = $path . '__workspace';
+
+    if (! Filesystem::pathExists($path)) {
+      $future = new ExecFuture(
+        'git clone file://%s %s',
+        $origin_path,
+        $path);
+      $future->resolvex();
+    }
+
+    self::obtainLock($path .'/.git/phabricator_lockfile');
+
+    $workspace = new ArcanistGitAPI($path);
+    $workspace->execxLocal('clean -fd');
+    $workspace->execxLocal('checkout master');
+    $workspace->execxLocal('fetch');
+    $workspace->execxLocal('reset --hard origin/master');
+    $workspace->reloadWorkingCopy();
+
+    return $workspace;
+  }
+
+  private static function obtainLock($filename) {
+    $file = fopen($filename, 'c');
+    if ($file === false) {
+      throw new Exception("Could not create lockfile");
+    }
+    $locked = flock($file, LOCK_EX | LOCK_NB);
+    if ($locked !== true) {
+      throw new Exception("Could not lock lockfile");
+    }
+    // ...and keep the lock for the remainder of run.
+  }
+}
Index: src/applications/differential/application/PhabricatorApplicationDifferential.php
===================================================================
--- src/applications/differential/application/PhabricatorApplicationDifferential.php
+++ src/applications/differential/application/PhabricatorApplicationDifferential.php
@@ -48,6 +48,8 @@
         'changeset/' => 'DifferentialChangesetViewController',
         'revision/edit/(?:(?P<id>[1-9]\d*)/)?'
           => 'DifferentialRevisionEditController',
+        'revision/land/'
+          => 'DifferentialRevisionLandController',
         'comment/' => array(
           'preview/(?P<id>[1-9]\d*)/' => 'DifferentialCommentPreviewController',
           'save/' => 'DifferentialCommentSaveController',
Index: src/applications/differential/controller/DifferentialRevisionLandController.php
===================================================================
--- /dev/null
+++ src/applications/differential/controller/DifferentialRevisionLandController.php
@@ -0,0 +1,142 @@
+<?php
+
+final class DifferentialRevisionLandController extends DifferentialController {
+
+  public function processRequest() {
+    $request = $this->getRequest();
+    $viewer = $request->getUser();
+
+    $revision_id = $request->getInt('revisionID');
+
+    if ($revision_id == null) {
+      throw new Exception('"');
+    }
+
+    list($error, $details) = $this->attemptLand($revision_id, $viewer);
+
+    if ($error === null) {
+      $title = "Success!";
+      $text = "Revision was successfully landed.";
+    } else {
+      $title = "Failed to land revision";
+      $text = hsprintf('%s<br>Details:<br><pre>%s</pre>', $error, $details);
+    }
+
+    $dialog = id(new AphrontDialogView())
+      ->setUser($viewer)
+      ->setTitle($title)
+      ->appendChild(phutil_tag('p', array(), $text));
+
+    return id(new AphrontDialogResponse())->setDialog($dialog);
+  }
+
+  private function attemptLand($revision_id, $viewer) {
+      $revision = id(new DifferentialRevisionQuery())
+        ->withIDs(array($revision_id))
+        ->setViewer($viewer)
+        ->executeOne();
+      if (!$revision) {
+        return array("revision $revision_id not found");
+      }
+
+      $status = $revision->getStatus();
+      if ($status != ArcanistDifferentialRevisionStatus::ACCEPTED) {
+        return array("Can only land Accepted revisions.");
+      }
+
+      // TODO assert user CAN_PUSH.
+
+
+      $repo = $revision->getRepository();
+
+      if ($repo === null) {
+        return array("revision is not attached to a repository.");
+      }
+
+      try {
+        $workspace = $this->getWorkspace($repo);
+      } catch (Exception $e) {
+        return array('Failed to allocate a workspace.', $e->getMessage());
+      }
+
+      try {
+        $this->commitRevisionToWorkspace($revision, $workspace, $viewer);
+      } catch (Exception $e) {
+        return array('Failed to commit patch.', $e->getMessage());
+      }
+
+      try {
+        $this->pushWorkspaceToHostedRepo($workspace);
+      } catch (Exception $e) {
+        return array('Failed to push changes upstream.', $e->getMessage());
+      }
+
+    return array();
+  }
+
+  function getWorkspace($repo) {
+    return DifferentialGetWorkingCopy::getCleanGitWorkspace($repo);
+  }
+
+  function commitRevisionToWorkspace($revision, $workspace, $viewer) {
+    $diff = $revision->loadActiveDiff();
+    $diff_id = $diff->getID();
+
+    $call = new ConduitCall(
+      'differential.getrawdiff',
+      array(
+        'diffID'   => $diff_id,
+      ));
+
+    $call->setUser($viewer);
+    $raw_diff = $call->execute();
+
+    $missing_binary =
+      "\nindex "
+      . "0000000000000000000000000000000000000000.."
+      . "0000000000000000000000000000000000000000\n";
+    if (strpos($raw_diff, $missing_binary) !== false) {
+      throw new Exception("Patch is missing content for a binary file");
+    }
+
+    $tmp_file = new TempFile();
+    Filesystem::writeFile($tmp_file, $raw_diff);
+
+    $workspace->execxLocal('apply --index %s', $tmp_file);
+
+    $workspace->reloadWorkingCopy();
+
+    $call = new ConduitCall(
+      'differential.getcommitmessage',
+      array(
+        'revision_id'   => $revision->getID(),
+      ));
+
+    $call->setUser($viewer);
+    $message = $call->execute();
+
+    $author = id(new PhabricatorUser())->loadOneWhere(
+      'phid = %s',
+      $revision->getAuthorPHID());
+
+    $author_string = sprintf(
+      '%s <%s>',
+      $author->getRealName(),
+      $author->loadPrimaryEmailAddress());
+
+    $workspace->execxLocal(
+      '-c user.name=%s -c user.email=%s commit --message=%s --author=%s',
+      // -c will set the 'committer'
+      $viewer->getRealName(),
+      $viewer->loadPrimaryEmailAddress(),
+      $message,
+      $author_string);
+  }
+
+  private function pushWorkspaceToHostedRepo(ArcanistGitAPI $workspace) {
+    // This will only work for bare, hosted repos, which I'm guessing is good enough.
+    $workspace->execxLocal(
+      "push origin HEAD:master");
+  }
+}
+
Index: src/applications/differential/controller/DifferentialRevisionViewController.php
===================================================================
--- src/applications/differential/controller/DifferentialRevisionViewController.php
+++ src/applications/differential/controller/DifferentialRevisionViewController.php
@@ -535,6 +535,13 @@
       'href'  => $request_uri->alter('download', 'true')
     );
 
+    // TODO test for policy, state and repo kind.
+    $links[] = array(
+      'icon'  => 'none',
+      'name'  => pht('Land this revision'),
+      'href'  => "/differential/revision/land/?revisionID=${revision_id}"
+    );
+
     return $links;
   }