diff --git a/src/as/com/threerings/util/Set.as b/src/as/com/threerings/util/Set.as
new file mode 100644
index 000000000..1d22624f2
--- /dev/null
+++ b/src/as/com/threerings/util/Set.as
@@ -0,0 +1,57 @@
+//
+// $Id: Set.as 4848 2007-10-18 23:55:26Z tim $
+//
+// Narya library - tools for developing networked games
+// Copyright (C) 2002-2007 Three Rings Design, Inc., All Rights Reserved
+// http://www.threerings.net/code/narya/
+//
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published
+// by the Free Software Foundation; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.threerings.util {
+
+public interface Set
+{
+    /**
+     * Adds the specified element to the set if it's not already present.
+     * Returns true if the set did not already contain the specified element.
+     */
+    function add (o :Object) :Boolean;
+
+    /**
+     * Removes the specified element from this set if it is present.
+     * Returns true if the set contained the specified element.
+     */
+    function remove (o :Object) :Boolean;
+
+    /** Remove all elements from this set. */
+    function clear () :void;
+
+    /** Returns true if this set contains the specified element. */
+    function contains (o :Object) :Boolean;
+
+    /** Retuns the number of elements in this set. */
+    function size () :int; // @TSC - should this be uint?
+
+    /** Returns true if this set contains no elements. */
+    function isEmpty () :Boolean;
+
+    /**
+     * Returns all elements in the set in an Array.
+     * Modifying the returned Array will not modify the set.
+     */
+    function toArray () :Array;
+}
+
+}