Non-thermal particles in the intergalactic and intracluster medium

I present a review of nonthermal processes in the large scale structure of the universe. After examining the properties of cosmological shock waves and their role as particle accelerators, I discuss the main observational facts, from radio to \gr and describe the processes that are thought be responsible for the observed nonthermal emissions. Finally, I emphasize the important role of $\gamma$-ray astronomy for the progress in the field. Non detections (upper limits) at these photon energies have already allowed us to draw important conclusions. Future observations will tell us more about the physical conditions in the intracluster medium, physics of shocks dissipation, aspects of CR acceleration.