  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 X-ray signatures of the thermal effects
of merger shocks will be discussed. X-ray observations of shocks can be used to
determine the geometry and kinematics of the merger. 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.
