  We apply the general theory of tensor products of modules for a vertex
operator algebra developed in our papers hep-th/9309076, hep-th/9309159,
hep-th/9401119, q-alg/9505018, q-alg/9505019 and q-alg/9505020 to the case of
the Wess-Zumino-Novikov-Witten models and related models in conformal field
theory. We show that for the category of modules for a vertex operator algebra
containing a subalgebra isomorphic to a tensor product of rational vertex
operator algebras associated to affine Lie algebras, the intertwining operators
among the modules have the associativity property, the category has a natural
structure of vertex tensor category, and a number of related results hold. We
obtain, as a corollary and special case, a construction of the
previously-studied braided tensor category structure on the category of finite
direct sums of standard (integrable highest weight) modules of a fixed positive
integral level for an affine Lie algebra.
