  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.
