We consider the
-theory of smooth
algebraic stacks, establish
and
operations, and show
that the higher
-theory of such
stacks is always a pre--ring,
and is a
-ring
if every coherent sheaf is the quotient of a vector bundle. As a consequence, we
are able to define Adams operations and absolute cohomology for smooth
algebraic stacks satisfying this hypothesis. We also obtain a comparison of the
absolute cohomology with the equivariant higher Chow groups in certain special
cases.