  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. The basic properties of cluster mergers and their
effects will be discussed. Mergers drive shocks in the intracluster gas, and
these shocks heat the intracluster gas, and should also accelerate nonthermal
relativistic particles. Mergers also produce distinctive features in the X-ray
images of clusters, including "cold fronts" and cool trails. Chandra and
XMM/Newton observations of the X-ray signatures of mergers will be discussed.
X-ray observations of shocks and cold fronts can be used to determine the
geometry and kinematics of the merger. As a result of particle acceleration in
shocks and turbulent acceleration following mergers, clusters of galaxies
should contain very large populations of relativistic electrons and ions.
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.
