  Representations of vertex operator algebras define sheaves of coinvariants
and conformal blocks on moduli of stable pointed curves. Assuming certain
finiteness and semisimplicity conditions, we prove that such sheaves satisfy
the factorization conjecture and consequently are vector bundles. Factorization
is essential to a recursive formulation of invariants, like ranks and Chern
classes, and to produce new constructions of rational conformal field theories
and cohomological field theories.
