  We introduce the main concepts and announce the main results in a theory of
tensor products for module categories for a vertex operator algebra. This
theory is being developed in a series of papers including hep-th 9309076 and
hep-th 9309159. The theory applies in particular to any ``rational'' vertex
operator algebra for which products of intertwining operators are known to be
convergent in the appropriate regions, including the vertex operator algebras
associated with the WZNW models, the minimal models and the moonshine module
for the Monster. In this paper, we provide background and motivation; we
present the main constructions and properties of the tensor product operation
associated with a particular element of a suitable moduli space of spheres with
punctures and local coordinates; we introduce the notion of ``vertex tensor
category,'' analogous to the notion of tensor category but based on this moduli
space; and we announce the results that the category of modules for a vertex
operator algebra of the type mentioned above admits a natural vertex tensor
category structure, and also that any vertex tensor category naturally produces
a braided tensor category structure.
