  We address the role of gamma-ray astronomy in the investigation of nonthermal
processes in the large scale structure of the universe. Based on EGRET upper
limits on nearby galaxy clusters (GCs) we constrain the acceleration efficiency
of CR electrons at intergalactic shocks to <=1 % than the shock ram pressure.
That implies a contribution to the cosmic gamma-ray background from
intergalactic shocks of order 25 % of the measured level. We model spatial and
spectral properties of nonthermal gamma-ray emission due to shock accelerated
cosmic-rays (CRs) in GCs and emphasize the importance of imaging capability of
upcoming gamma-ray facilities for a correct interpretation of the observational
results. GC observations at this photon energy will help us understand the
origin of the radio emitting particles, the possible level of CR pressure and
the strength of magnetic fields in intracluster environment and possibly will
allow us detect the accretion shocks.
