There are a couple of options I can think of. I think the best option would be to hook the CollectionChanged event of the Items collection of the QuickAccessToolbar (e.g. ((INotifyCollectionChanged)this.qat.Items).CollectionChanged += new NotifyCollectionChangedEventHandler(OnQatItemsChanged);). Another option might be to hook the ToolCloned event of the tools (or possibly hook it on the ribbon) but this may not give you the results you expect as this could be raised for the items within a ribbongroup when the ribbon group is added to the qat (or when its expanded and the associated group's items have changed).