diff --git a/lib/repl.js b/lib/repl.js
index 78171dab63..d0400235e7 100644
--- a/lib/repl.js
+++ b/lib/repl.js
@@ -46,6 +46,7 @@ exports.writer = util.inspect;
 function REPLServer(prompt, stream) {
   var self = this;
   if (!context) resetContext();
+  if (!exports.repl) exports.repl = this;
   self.context = context;
   self.buffered_cmd = '';
 
@@ -56,6 +57,9 @@ function REPLServer(prompt, stream) {
     return self.complete(text);
   });
 
+  this.commands = {};
+  defineDefaultCommands(this);
+
   if (rli.enabled && !disableColors) {
     // Turn on ANSI coloring.
     exports.writer = function(obj, showHidden, depth) {
@@ -86,7 +90,12 @@ function REPLServer(prompt, stream) {
 
     // Check to see if a REPL keyword was used. If it returns true,
     // display next prompt and return.
-    if (self.parseREPLKeyword(cmd) === true) return;
+    if (cmd && cmd.charAt(0) === '.') {
+      var matches = cmd.match(/^(\.[^\s]+)\s*(.*)$/);
+      var keyword = matches && matches[1];
+      var rest = matches && matches[2];
+      if (self.parseREPLKeyword(keyword, rest) === true) return;
+    }
 
     // The catchall for errors
     try {
@@ -185,7 +194,7 @@ REPLServer.prototype.complete = function (line) {
   var match = null;
   match = line.match(/^\s*(\.\w*)$/);
   if (match) {
-    completionGroups.push(['.break', '.clear', '.exit', '.help']);
+    completionGroups.push(Object.keys(this.commands));
     completeOn = match[1];
     if (match[1].length > 1) {
       filter = match[1];
@@ -397,34 +406,63 @@ REPLServer.prototype.complete = function (line) {
  * @returns {Boolean} If true it means don't continue parsing the command
  */
 
-REPLServer.prototype.parseREPLKeyword = function (cmd) {
-  var self = this;
-
-  switch (cmd) {
-  case ".break": 
-    // TODO remove me after 0.3.x
-    self.buffered_cmd = '';
-    self.displayPrompt();
-    return true;
-  case ".clear":
-    self.stream.write("Clearing context...\n");
-    self.buffered_cmd = '';
-    resetContext();
-    self.displayPrompt();
-    return true;
-  case ".exit":
-    self.stream.destroy();
-    return true;
-  case ".help":
-    self.stream.write(".clear\tBreak, and also clear the local context.\n");
-    self.stream.write(".exit\tExit the prompt\n");
-    self.stream.write(".help\tShow repl options\n");
-    self.displayPrompt();
+REPLServer.prototype.parseREPLKeyword = function (keyword, rest) {
+  var cmd = this.commands[keyword];
+  if (cmd) {
+    cmd.action.call(this, rest);
     return true;
   }
   return false;
 };
 
+REPLServer.prototype.defineCommand = function(keyword, cmd) {
+  if (typeof cmd === 'function') cmd = {action: cmd};
+  else if (typeof cmd.action !== 'function') {
+    throw new Error('bad argument, action must be a function');
+  }
+  this.commands['.' + keyword] = cmd;
+};
+
+function defineDefaultCommands(repl) {
+  // TODO remove me after 0.3.x
+  repl.defineCommand('break', {
+    help: 'Sometimes you get stuck, this gets you out',
+    action: function() {
+      this.buffered_cmd = '';
+      this.displayPrompt();
+    }
+  });
+
+  repl.defineCommand('clear', {
+    help: 'Break, and also clear the local context',
+    action: function() {
+      this.stream.write("Clearing context...\n");
+      this.buffered_cmd = '';
+      resetContext();
+      this.displayPrompt();
+    }
+  });
+
+  repl.defineCommand('exit', {
+    help: 'Exit the repl',
+    action: function() {
+      this.stream.destroy();
+    }
+  });
+
+  repl.defineCommand('help', {
+    help: 'Show repl options',
+    action: function() {
+      var self = this;
+      Object.keys(this.commands).sort().forEach(function(name) {
+        var cmd = self.commands[name];
+        self.stream.write(name + "\t" + (cmd.help || '') + "\n");
+      });
+      this.displayPrompt();
+    }
+  });
+}
+
 function trimWhitespace (cmd) {
   var trimmer = /^\s*(.+)\s*$/m,
     matches = trimmer.exec(cmd);