  The category of $C^*$-algebras is blessed with many different tensor
products. In contrast, virtually the only tensor product ever used in the
category of von Neumann algebras is the normal spatial tensor product. We
propose a definition of what a generic tensor product in this category should
be. We call these weak* tensor products.
  For von Neumann algebras $M$ and $N$, there are, in general, many choices of
weak* tensor completions of the algebraic tensor product $M\odot N$. In fact,
we demonstrate that $M$ has the property that $M\odot N$ has a unique weak*
tensor product completion for every von Neumann algebra $N$ if and only if $M$
is completely atomic, i.e., is a direct product of type I factors. This in
particular implies that even abelian von Neumann algebras need not have this
property. As an application of the theory developed throughout the paper, we
construct $2^{\mathfrak c}$ nonequivalent weak* tensor product completions of
$L^\infty(\mathbb R)\odot L^\infty(\mathbb R)$.
