  The density budget of the Universe is reviewed, and then specific particle
candidates for non-bayonic dark matter are introduced, with emphasis on the
relevance of cosmic-ray physics. The sizes of the neutrino masses indicated by
recent atmospheric and solar neutrino experiments may be too small to
contribute much hot dark matter. My favoured candidate for the dominant cold
dark matter is the lightest supersymmetric particle, which probably weighs
between about 50 GeV and about 600 GeV. Strategies to search for it via cosmic
rays due to annihilations in the halo, Sun and Earth, or via direct scattering
experiments, are mentioned. Possible superheavy relic particles are also
discussed, in particular metastable string- or M-theory cryptons, that may be
responsible for the ultra-high-energy cosmic rays. Finally, it is speculated
that a non-zero contribution to the cosmological vacuum energy might result
from incomplete relaxation of the quantum-gravitational vacuum.

Astrophysics