Non-thermal phenomena in galaxy clusters

The recent evidences of the presence of magnetic fields and relativistic particles in galaxy clusters are reviewed. The existence of microG-level magnetic fields in cluster atmospheres appears well established from the detection of diffuse radio emission and from studies of Rotation Measure. The fact that the diffuse radio emission is not common in clusters favours the hypothesis that the population of relativistic particles, produced during the cluster formation by AGNs or star formation, are reaccelerated by recent cluster merger processes.