  We compare two approaches to the homotopy theory of infinity-operads. One of
them, the theory of dendroidal sets, is based on an extension of the theory of
simplicial sets and infinity-categories which replaces simplices by trees. The
other is based on a certain homotopy theory of marked simplicial sets over the
nerve of Segal's category Gamma. In this paper we prove that for operads
without constants these two theories are equivalent, in the precise sense of
the existence of a zig-zag of Quillen equivalences between the respective model
categories.
