Discontinuous Petrov-Galerkin (DPG) methods are new discontinuous Galerkin methods [3,4,5,6,7,8] with interesting properties. In this article we consider a domain decomposition preconditioner for a DPG method for the Poisson problem.Let Ω be a polyhedral domain in R d (d = 2, 3), Ω h be a simplicial triangulation of Ω . Following the notation in [8], the model Poisson problem (in an ultraweak formulation) is to find