diff --git a/lib/readline.js b/lib/readline.js
index 7c6f416d90..2562124b60 100644
--- a/lib/readline.js
+++ b/lib/readline.js
@@ -16,12 +16,13 @@ var stdio = process.binding('stdio');
 
 
 
-exports.createInterface = function (output) {
-  return new Interface(output);
+exports.createInterface = function (output, completer) {
+  return new Interface(output, completer);
 };
 
-function Interface (output) {
+function Interface (output, completer) {
   this.output = output;
+  this.completer = completer;
 
   this.setPrompt("node> ");
 
@@ -126,6 +127,48 @@ Interface.prototype._normalWrite = function (b) {
   this.emit('line', b.toString());
 };
 
+Interface.prototype._insertString = function (c) {
+  //BUG: Problem when adding tabs with following content.
+  //     Perhaps the bug is in _refreshLine(). Not sure.
+  //     A hack would be to insert spaces instead of literal '\t'.
+  if (this.cursor < this.line.length) {
+    var beg = this.line.slice(0, this.cursor);
+    var end = this.line.slice(this.cursor, this.line.length);
+    this.line = beg + c + end;
+    this.cursor += c.length;
+    this._refreshLine();
+  } else {
+    this.line += c;
+    this.cursor += c.length;
+    this.output.write(c);
+  }
+};
+
+Interface.prototype._tabComplete = function () {
+  var self = this;
+
+  var rv = this.completer(self.line.slice(0, self.cursor));
+  var completions = rv[0],
+      completeOn = rv[1];  // the text that was completed
+  if (completions && completions.length) {
+    // Apply/show completions.
+    if (completions.length === 1) {
+      self._insertString(completions[0].slice(completeOn.length));
+      self._refreshLine();
+    } else {
+      //TODO: Multi-column display. Request to show if more than N completions.
+      self.output.write("\n");
+      completions.forEach(function (c) {
+        //TODO: try using '\r\n' instead of the following goop for getting to column 0
+        self.output.write('\x1b[0G');
+        self.output.write(c + "\n");
+      })
+      self.output.write('\n');
+      self._refreshLine();
+    }
+  }
+};
+
 Interface.prototype._historyNext = function () {
   if (this.historyIndex > 0) {
     this.historyIndex--;
@@ -228,6 +271,12 @@ Interface.prototype._ttyWrite = function (b) {
       this._historyNext();
       break;
 
+    case 9: // tab, completion
+      if (this.completer) {
+        this._tabComplete();
+      }
+      break;
+
     case 16: // control-p, previous history item
       this._historyPrev();
       break;
@@ -270,16 +319,12 @@ Interface.prototype._ttyWrite = function (b) {
 
     default:
       var c = b.toString('utf8');
-      if (this.cursor < this.line.length) {
-        var beg = this.line.slice(0, this.cursor);
-        var end = this.line.slice(this.cursor, this.line.length);
-        this.line = beg + c + end;
-        this.cursor += c.length;
-        this._refreshLine();
-      } else {
-        this.line += c;
-        this.cursor += c.length;
-        this.output.write(c);
+      var lines = c.split(/\r\n|\n|\r/);
+      for (var i = 0; i < lines.length; i++) {
+        if (i > 0) {
+          this._ttyWrite(new Buffer([13]));
+        }
+        this._insertString(lines[i]);
       }
       break;
   }
diff --git a/lib/repl.js b/lib/repl.js
index 52ae11c3a3..c0bd82b36c 100644
--- a/lib/repl.js
+++ b/lib/repl.js
@@ -49,7 +49,9 @@ function REPLServer(prompt, stream) {
   self.stream = stream || process.openStdin();
   self.prompt = prompt || "node> ";
 
-  var rli = self.rli = rl.createInterface(self.stream);
+  var rli = self.rli = rl.createInterface(self.stream, function (text) {
+    return self.complete(text);
+  });
   rli.setPrompt(self.prompt);
 
   self.stream.addListener("data", function (chunk) {
@@ -135,6 +137,174 @@ REPLServer.prototype.displayPrompt = function () {
 REPLServer.prototype.readline = function (cmd) {
 };
 
+/**
+ * Provide a list of completions for the given leading text. This is
+ * given to the readline interface for handling tab completion.
+ *
+ * @param {line} The text (preceding the cursor) to complete
+ * @returns {Array} Two elements: (1) an array of completions; and
+ *    (2) the leading text completed.
+ *
+ * Example:
+ *  complete('var foo = sys.')
+ *    -> [['sys.print', 'sys.debug', 'sys.log', 'sys.inspect', 'sys.pump'],
+ *        'sys.' ]
+ *
+ * TODO: add warning about exec'ing code... property getters could be run
+ */
+
+REPLServer.prototype.complete = function (line) {
+  // TODO: special completion in `require` calls.
+
+  var completions,
+      completionGroups = [],  // list of completion lists, one for each inheritance "level"
+      completeOn,
+      match, filter, i, j, group, c;
+
+  // REPL comments (e.g. ".break").
+  var match = null;
+  match = line.match(/^\s*(\.\w*)$/);
+  if (match) {
+    completionGroups.push(['.break', '.clear', '.exit', '.help']);
+    completeOn = match[1];
+    if (match[1].length > 1) {
+      filter = match[1];
+    }
+  }
+
+  // Handle variable member lookup.
+  // We support simple chained expressions like the following (no function
+  // calls, etc.). That is for simplicity and also because we *eval* that
+  // leading expression so for safety (see WARNING above) don't want to
+  // eval function calls.
+  //
+  //   foo.bar<|>     # completions for 'foo' with filter 'bar'
+  //   spam.eggs.<|>  # completions for 'spam.eggs' with filter ''
+  //   foo<|>         # all scope vars with filter 'foo'
+  //   foo.<|>        # completions for 'foo' with filter ''
+  else if (line.length === 0 || line[line.length-1].match(/\w|\./)) {
+    var simpleExpressionPat = /(([a-zA-Z_]\w*)\.)*([a-zA-Z_]\w*)\.?$/;
+    match = simpleExpressionPat.exec(line);
+    if (line.length === 0 || match) {
+      var expr;
+      completeOn = (match ? match[0] : "");
+      if (line.length === 0) {
+        filter = "";
+        expr = "";
+      } else if (line[line.length-1] === '.') {
+        filter = "";
+        expr = match[0].slice(0, match[0].length-1);
+      } else {
+        var bits = match[0].split('.');
+        filter = bits.pop();
+        expr = bits.join('.');
+      }
+      //console.log("expression completion: completeOn='"+completeOn+"' expr='"+expr+"'");
+
+      // Resolve expr and get its completions.
+      var obj, memberGroups = [];
+      if (!expr) {
+        completionGroups.push(Object.getOwnPropertyNames(this.context));
+        // Global object properties
+        // (http://www.ecma-international.org/publications/standards/Ecma-262.htm)
+        completionGroups.push(["NaN", "Infinity", "undefined",
+          "eval", "parseInt", "parseFloat", "isNaN", "isFinite", "decodeURI",
+          "decodeURIComponent", "encodeURI", "encodeURIComponent",
+          "Object", "Function", "Array", "String", "Boolean", "Number",
+          "Date", "RegExp", "Error", "EvalError", "RangeError",
+          "ReferenceError", "SyntaxError", "TypeError", "URIError",
+          "Math", "JSON"]);
+        // Common keywords. Exclude for completion on the empty string, b/c
+        // they just get in the way.
+        if (filter) {
+          completionGroups.push(["break", "case", "catch", "const",
+            "continue", "debugger", "default", "delete", "do", "else", "export",
+            "false", "finally", "for", "function", "if", "import", "in",
+            "instanceof", "let", "new", "null", "return", "switch", "this",
+            "throw", "true", "try", "typeof", "undefined", "var", "void",
+            "while", "with", "yield"])
+        }
+      } else {
+        try {
+          obj = evalcx(expr, this.context, "repl");
+        } catch (e) {
+          //console.log("completion eval error, expr='"+expr+"': "+e);
+        }
+        if (obj != null) {
+          //TODO: The following, for example, misses "Object.isSealed". Is there
+          //      a way to introspec those? Need to hardcode?
+          if (typeof obj === "object" || typeof obj === "function") {
+            memberGroups.push(Object.getOwnPropertyNames(obj));
+          }
+          var p = obj.constructor.prototype; // works for non-objects
+          try {
+            var sentinel = 5;
+            while (p !== null) {
+              memberGroups.push(Object.getOwnPropertyNames(p));
+              p = Object.getPrototypeOf(p);
+              // Circular refs possible? Let's guard against that.
+              sentinel--;
+              if (sentinel <= 0) {
+                break;
+              }
+            }
+          } catch (e) {
+            //console.log("completion error walking prototype chain:" + e);
+          }
+        }
+
+        if (memberGroups.length) {
+          for (i = 0; i < memberGroups.length; i++) {
+            completionGroups.push(memberGroups[i].map(function(member) {
+              return expr + '.' + member;
+            }));
+          }
+          if (filter) {
+            filter = expr + '.' + filter;
+          }
+        }
+      }
+    }
+  }
+
+  // Filter, sort (within each group), uniq and merge the completion groups.
+  if (completionGroups.length && filter) {
+    var newCompletionGroups = [];
+    for (i = 0; i < completionGroups.length; i++) {
+      group = completionGroups[i].filter(function(elem) {
+        return elem.indexOf(filter) == 0;
+      });
+      if (group.length) {
+        newCompletionGroups.push(group);
+      }
+    }
+    completionGroups = newCompletionGroups;
+  }
+  if (completionGroups.length) {
+    var uniq = {};  // unique completions across all groups
+    completions = [];
+    // Completion group 0 is the "closest" (least far up the inheritance chain)
+    // so we put its completions last: to be closest in the REPL.
+    for (i = completionGroups.length - 1; i >= 0; i--) {
+      group = completionGroups[i];
+      group.sort();
+      for (var j = 0; j < group.length; j++) {
+        c = group[j];
+        if (!uniq.hasOwnProperty(c)) {
+          completions.push(c);
+          uniq[c] = true;
+        }
+      }
+      completions.push(""); // separator btwn groups
+    }
+    while (completions.length && completions[completions.length-1] === "") {
+      completions.pop();
+    }
+  }
+
+  return [completions || [], completeOn];
+};
+
 /**
  * Used to parse and execute the Node REPL commands.
  *