  The search for gamma radiation in clusters of galaxies represents a precious
tool to investigate the history of these large scale structures. Clusters or
sources within them accelerate cosmic rays, as demonstrated by the detection of
radio halos, hard X-rays and UV emission, and confine them over cosmological
time scales. Nonthermal and thermal phenomena may be closely related and
observations of gamma rays may tell us about this link. In this paper we review
the physics of cosmic ray acceleration and confinement in clusters of galaxies
and the related gamma ray signatures. In particular we describe in some detail
the role of cluster mergers for the acceleration of nonthermal particles. The
perspectives for gamma ray detection with GLAST and with ground based detectors
are also discussed.
