  We define for every dendroidal set X a chain complex and show that this
assignment determines a left Quillen functor. Then we define the homology
groups $H_n(X)$ as the homology groups of this chain complex. This generalizes
the homology of simplicial sets. Our main result is that the homology of X is
isomorphic to the homology of the associated spectrum K(X) as discussed in
earlier work of the authors. Since these homology groups are sometimes
computable we can identify some spectra K(X) which we could not identify
before.
