LAUSR

We introduce and study a homology theory of crossed modules with coefficients in an abelian crossed module. We discuss the basic properties of these new homology groups and give some applications. We then restrict our attention to the case of integral coefficients. In this case we regain the homology of crossed modules originally defined by Baues and further developed by Ellis. We show that it is an instance of Barr–Beck comonadic homology, so that we may use a result of Everaert and Gran to obtain Hopf formulae in all dimensions.