  Dark matter (comprising a quarter of the Universe) is usually assumed to be
due to one and only one weakly interacting particle which is neutral and
absolutely stable. We consider the possibility that there are several
coexisting dark-matter particles, and explore in some detail the generic case
where there are two. We discuss how the second dark-matter particle may relax
the severe constraints on the parameter space of the Minimal Supersymmetric
Standard Model, as well as other verifiable predictions in both direct and
indirect search experiments.
