diff --git a/src/repository/api/ArcanistGitAPI.php b/src/repository/api/ArcanistGitAPI.php
--- a/src/repository/api/ArcanistGitAPI.php
+++ b/src/repository/api/ArcanistGitAPI.php
@@ -16,6 +16,9 @@
    */
   const GIT_MAGIC_ROOT_COMMIT = '4b825dc642cb6eb9a060e54bf8d69288fbee4904';
 
+  private $symbolicHeadCommit = 'HEAD';
+  private $resolvedHeadCommit;
+
   public static function newHookAPI($root) {
     return new ArcanistGitAPI($root);
   }
@@ -106,7 +109,8 @@
       // this as being the commits X and Y. If we log "B..Y", we only show
       // Y. With "Y --not B", we show X and Y.
 
-      $against = csprintf('%s --not %s', 'HEAD', $this->getBaseCommit());
+      $against = csprintf('%s --not %s',
+        $this->getHeadCommit(), $this->getBaseCommit());
     }
 
     // NOTE: Windows escaping of "%" symbols apparently is inherently broken;
@@ -161,8 +165,9 @@
       }
 
       list($err, $merge_base) = $this->execManualLocal(
-        'merge-base %s HEAD',
-        $symbolic_commit);
+        'merge-base %s %s',
+        $symbolic_commit,
+        $this->getHeadCommit());
       if ($err) {
         throw new ArcanistUsageException(
           "Unable to find any git commit named '{$symbolic_commit}' in ".
@@ -170,8 +175,8 @@
       }
 
       $this->setBaseCommitExplanation(
-        "it is the merge-base of '{$symbolic_commit}' and HEAD, as you ".
-        "explicitly specified.");
+        "it is the merge-base of '{$symbolic_commit}' and ".
+        "{$this->symbolicHeadCommit}, as you explicitly specified.");
       return trim($merge_base);
     }
 
@@ -301,6 +306,43 @@
     return trim($merge_base);
   }
 
+  public function getHeadCommit() {
+    if (!$this->supportsCommitRanges()) {
+      throw new ArcanistCapabilityNotSupportedException($this);
+    }
+
+    if ($this->resolvedHeadCommit === null) {
+      $this->resolvedHeadCommit =
+        $this->resolveCommit($this->symbolicHeadCommit);
+    }
+
+    return $this->resolvedHeadCommit;
+  }
+
+  final public function setHeadCommit($symbolic_commit) {
+    $this->symbolicHeadCommit = $symbolic_commit;
+    $this->reloadCommitRange();
+    return $this;
+  }
+
+  /** Translates a symbolic commit (HEAD^) to a commit identifier
+   * @param $symbolic_commit
+   * @return string the commit SHA
+   */
+  private function resolveCommit($symbolic_commit) {
+    list($err, $merge_base) = $this->execManualLocal(
+      'rev-parse %s',
+      $symbolic_commit);
+
+    if ($err) {
+      throw new ArcanistUsageException(
+        "Unable to find any git commit named '{$symbolic_commit}' in ".
+        "this repository.");
+    }
+
+    return trim($merge_base);
+  }
+
   private function getDiffFullOptions($detect_moves_and_renames = true) {
     $options = array(
       self::getDiffBaseOptions(),
@@ -335,8 +377,9 @@
   public function getFullGitDiff() {
     $options = $this->getDiffFullOptions();
     list($stdout) = $this->execxLocal(
-      "diff {$options} %s --",
-      $this->getBaseCommit());
+      "diff {$options} %s..%s --",
+      $this->getBaseCommit(),
+      $this->getHeadCommit());
     return $stdout;
   }
 
@@ -401,8 +444,9 @@
     } else {
       // 2..N commits.
       list($stdout) = $this->execxLocal(
-        'log --first-parent --format=medium %s..HEAD',
-        $this->getBaseCommit());
+        'log --first-parent --format=medium %s..%s',
+        $this->getBaseCommit(),
+        $this->getHeadCommit());
     }
     return $stdout;
   }
diff --git a/src/repository/api/ArcanistRepositoryAPI.php b/src/repository/api/ArcanistRepositoryAPI.php
--- a/src/repository/api/ArcanistRepositoryAPI.php
+++ b/src/repository/api/ArcanistRepositoryAPI.php
@@ -575,6 +575,10 @@
     return $this;
   }
 
+  public function setHeadCommit($symbolic_commit) {
+    throw new ArcanistCapabilityNotSupportedException($this);
+  }
+
   final public function getBaseCommit() {
     if (!$this->supportsCommitRanges()) {
       throw new ArcanistCapabilityNotSupportedException($this);
@@ -588,6 +592,10 @@
     return $this->resolvedBaseCommit;
   }
 
+  public function getHeadCommit() {
+    throw new ArcanistCapabilityNotSupportedException($this);
+  }
+
   final public function reloadCommitRange() {
     $this->resolvedBaseCommit = null;
     $this->baseCommitExplanation = null;
diff --git a/src/workflow/ArcanistDiffWorkflow.php b/src/workflow/ArcanistDiffWorkflow.php
--- a/src/workflow/ArcanistDiffWorkflow.php
+++ b/src/workflow/ArcanistDiffWorkflow.php
@@ -395,6 +395,11 @@
         ),
       ),
       '*' => 'paths',
+      'range' => array(
+        'param' => 'range',
+        'help' => 'specify a commit range to include (BASE..HEAD)',
+        'supports' => array('git'),
+      )
     );
 
     if (phutil_is_windows()) {
@@ -433,8 +438,20 @@
         array_unshift($argv, '--ansi');
       }
 
-      if ($this->getRepositoryAPI()->supportsCommitRanges()) {
-        $this->getRepositoryAPI()->getBaseCommit();
+      $repo = $this->getRepositoryAPI();
+      $range = $this->getArgument('range', null);
+      $range_supported = $repo->supportsCommitRanges();
+      if ($range) {
+        if (!$range_supported) {
+          throw new Exception('ranged are not supported');
+        }
+
+        list($base, $head) = preg_split('(\\.\\.)', $range);
+        $repo->setHeadCommit($head);
+        $repo->setBaseCommit($base);
+
+      } else if ($range_supported) {
+        $repo->getBaseCommit();
       }
 
       $script = phutil_get_library_root('arcanist').'/../scripts/arcanist.php';
@@ -661,7 +678,9 @@
         if ($repository_api instanceof ArcanistSubversionAPI) {
           $repository_api->limitStatusToPaths($this->getArgument('paths'));
         }
-        $this->requireCleanWorkingCopy();
+        if (!$this->getArgument('range')) {
+          $this->requireCleanWorkingCopy();
+        }
       } catch (ArcanistUncommittedChangesException $ex) {
         if ($repository_api instanceof ArcanistMercurialAPI) {
           $use_dirty_changes = false;
@@ -1216,7 +1235,8 @@
   private function runLint() {
     if ($this->getArgument('nolint') ||
         $this->getArgument('only') ||
-        $this->isRawDiffSource()) {
+        $this->isRawDiffSource() ||
+        $this->getArgument('range')) {
       return ArcanistLintWorkflow::RESULT_SKIP;
     }
 
@@ -1297,7 +1317,8 @@
   private function runUnit() {
     if ($this->getArgument('nounit') ||
         $this->getArgument('only') ||
-        $this->isRawDiffSource()) {
+        $this->isRawDiffSource() ||
+        $this->getArgument('range')) {
       return ArcanistUnitWorkflow::RESULT_SKIP;
     }