diff --git a/src/workflow/ArcanistPasteWorkflow.php b/src/workflow/ArcanistPasteWorkflow.php
--- a/src/workflow/ArcanistPasteWorkflow.php
+++ b/src/workflow/ArcanistPasteWorkflow.php
@@ -9,6 +9,7 @@
   private $language;
   private $title;
   private $json;
+  private $edit;
 
   public function getWorkflowName() {
     return 'paste';
@@ -18,6 +19,7 @@
     return phutil_console_format(<<<EOTEXT
       **paste** [--title __title__] [--lang __language__] [--json]
       **paste** __id__ [--json]
+      **paste** __id__ --edit [--title __title__] [--lang __language__] [--json]
 EOTEXT
       );
   }
@@ -33,6 +35,10 @@
           To retrieve a paste, specify the paste ID:
 
             $ arc paste P123
+
+          To edit a paste, specify the paste ID and --edit option:
+
+            $ cat list_of_ducks.txt | arc paste P123 --edit
 EOTEXT
       );
   }
@@ -50,6 +56,9 @@
       'json' => array(
         'help' => 'Output in JSON format.',
       ),
+      'edit' => array(
+        'help' => 'Edit an existing paste.',
+      ),
       '*' => 'argv',
     );
   }
@@ -62,6 +71,7 @@
     $this->language = $this->getArgument('lang');
     $this->title    = $this->getArgument('title');
     $this->json     = $this->getArgument('json');
+    $this->edit     = $this->getArgument('edit');
 
     $argv = $this->getArgument('argv');
     if (count($argv) > 1) {
@@ -73,11 +83,16 @@
       }
       $this->id = (int)ltrim($id, 'P');
 
-      if ($this->language || $this->title) {
+      if (!$this->getEdit() && ($this->language || $this->title)) {
         throw new ArcanistUsageException(
-          'Use options --lang and --title only when creating pastes.');
+          'Use options --lang and --title only when creating or editing '.
+          'pastes.');
       }
     }
+
+    if ($this->getEdit() && !$this->id) {
+      throw new ArcanistUsageException('Specify a paste to edit.');
+    }
   }
 
   private function getTitle() {
@@ -92,9 +107,15 @@
     return $this->json;
   }
 
+  private function getEdit() {
+    return $this->edit;
+  }
+
   public function run() {
 
-    if ($this->id) {
+    if ($this->getEdit()) {
+      return $this->editPaste();
+    } else if ($this->id) {
       return $this->getPaste();
     } else {
       return $this->createPaste();
@@ -148,4 +169,28 @@
     return 0;
   }
 
+  private function editPaste() {
+    $conduit = $this->getConduit();
+
+    // Avoid confusion when people type "arc paste" with nothing else.
+    $this->writeStatusMessage("Reading paste from stdin...\n");
+
+    $info = $conduit->callMethodSynchronous(
+      'paste.edit',
+      array(
+        'paste_id'  => $this->id,
+        'content'   => file_get_contents('php://stdin'),
+        'title'     => $this->getTitle(),
+        'language'  => $this->getLanguage(),
+      ));
+
+    if ($this->getArgument('json')) {
+      echo json_encode($info)."\n";
+    } else {
+      echo $info['objectName'].': '.$info['uri']."\n";
+    }
+
+    return 0;
+  }
+
 }