Cosmic Rays and Non-Thermal Emission in Galaxy Clusters

We discuss the origin of thermal and non-thermal phenomena in galaxy clusters. Specifically, we present some expectations for the non-thermal emission (from radio to gamma ray wavelenghts) expected in a model in which secondary electrons are produced via $pp$ collisions in the intracluster medium. We also discuss the possibility to test this cosmic ray model in the light of recent data on radio halos and hard X-ray excesses found in nearby galaxy clusters.