diff --git a/mailnews/addrbook/public/nsIAddrBookSession.idl b/mailnews/addrbook/public/nsIAddrBookSession.idl
new file mode 100644
index 00000000000..3dc80ce774b
--- /dev/null
+++ b/mailnews/addrbook/public/nsIAddrBookSession.idl
@@ -0,0 +1,47 @@
+/* -*- Mode: IDL; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ *
+ * The contents of this file are subject to the Netscape Public License
+ * Version 1.0 (the "NPL"); you may not use this file except in
+ * compliance with the NPL.  You may obtain a copy of the NPL at
+ * http://www.mozilla.org/NPL/
+ *
+ * Software distributed under the NPL is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the NPL
+ * for the specific language governing rights and limitations under the
+ * NPL.
+ *
+ * The Initial Developer of this code under the NPL is Netscape
+ * Communications Corporation.  Portions created by Netscape are
+ * Copyright (C) 1998 Netscape Communications Corporation.  All Rights
+ * Reserved.
+ */
+
+#include "nsISupports.idl"
+
+/*
+ * The mail session is a replacement for the old 4.x MSG_Master object. It
+ * contains mail session generic information such as the account manager, etc
+ * I'm starting this off as an empty interface and as people feel they need to
+ * add more information to it, they can. I think this is a better approach
+ * than trying to port over the old MSG_Master in its entirety as that had a
+ * lot of cruft in it....
+ */
+
+#include "nsISupports.idl"
+#include "nsIAbListener.idl"
+#include "nsIAbDirectory.idl"
+#include "nsIAbCard.idl"
+
+[scriptable, uuid(C5339441-303F-11d3-9E13-00A0C92B5F0D)]
+interface nsIAddrBookSession : nsISupports {
+
+  void AddAddressBookListener(in nsIAbListener listener);
+  void RemoveAddressBookListener(in nsIAbListener listener);
+  void NotifyItemPropertyChanged(in nsISupports item,
+                                 in string property,
+                                 in string oldValue,
+                                 in string newValue);
+  void NotifyDirectoryItemAdded(in nsIAbDirectory directory, in nsISupports item);
+  void NotifyDirectoryItemDeleted(in nsIAbDirectory directory, in nsISupports item);
+};
+