  Clusters of galaxies generally form by the gravitational merger of smaller
clusters and groups. Major cluster mergers are the most energetic events in the
Universe since the Big Bang. Mergers drive shocks into the intracluster gas,
and these shocks heat the intracluster gas, and should also accelerate
nonthermal relativistic particles. The thermal effects of merger shocks will be
briefly discussed. Mergers can increase the temperature and X-ray luminosities
of clusters, and this may affect statistical conclusions about cosmological
parameters. As a result of particle acceleration in shocks, clusters of
galaxies should contain very large populations of relativistic electrons and
ions. Electrons with Lorentz factors gamma~300 (energies E = gamma m_e c^2 ~
150 MeV) are expected to be particularly common. Observations and models for
the radio, extreme ultraviolet, hard X-ray, and gamma-ray emission from
nonthermal particles accelerated in these shocks will also be described. The
predicted gamma-ray fluxes of clusters should make them easily observable with
GLAST. Chandra X-ray observations of the interaction between the radio lobes
and cooling flow gas in Abell 2052 are also discussed briefly.
