In this paper we introduce and study a cohomology theory {Hn(-, A)} for simplicial sets with coefficients in symmetric categorical groups A. We associate to a symmetric categorical group A a sequence of simplicial sets {K(A, n)}n0, which allows us to give a representation theorem for our cohomology. Moreover, we prove that for any n 3, the functor K(-, n) is right adjoint to the functor n, where n(X