  Some particle candidates for dark matter are reviewed in the light of recent
experimental and theoretical developments. Models for massive neutrinos are
discussed in the light of the recent atmospheric-neutrino data, and used to
motivate comments on the plausibility of different solutions to the solar
neutrino problem. Arguments are given that the lightest supersymmetric particle
should be a neutralino \chi, and accelerator and astrophysical constraints used
to suggest that 50 GeV \lappeq m_\chi \lappeq 600 GeV. Minimizing the fine
tuning of the gauge hierarchy favours \Omega_\chi h^2 \sim 0.1. The possibility
of superheavy relic particles is mentioned, and candidates from string and $M$
theory are reviewed. Finally, the possibility of non-zero vacuum energy is
discussed: its calculation is a great opportunity for a quantum theory of
gravity, and the possibility that it is time dependent should not be forgotten.
