It is really the same thing you would do if you were using a Menu or Toolbar. You would need to define an InputBinding at the Window level. There is more information/examples in MS documentation - http://msdn.microsoft.com/en-us/library/ms752308.aspx. Note, the xamRibbon tools in the ribbon group will not show a mnemonic character since tools in Office Ribbon do not show mnemonics - instead the keytips are used when in keytip mode (e.g. pressing and releasing Alt).