The Intra-Cluster Medium
  The Intra-Cluster Medium (ICM) is a rarefied, hot, highly ionized, metal rich, weakly magnetized plasma. In these proceeding, after having reviewed some basic ICM properties, I discuss recent results obtained with the BeppoSAX, XMM-Newton and Chandra satellites. These results are summarized in the following five points. 1) Currently available hard X-ray data does not allow us to constrain B fields in radio halos, the advent of hard X-ray telescopes in a few years may change the situation substantially. 2) There is mounting evidence that temperature profiles of clusters at large radii decline; however investigation of the outermost regions will have to await a new generation of yet unplanned but technologically feasible experiments. 3) The ICM is polluted with metals, the enrichment has probably occurred early on in the cluster's life. The abundance excess observed at the center of CC clusters is due to the giant elliptical always found in these systems. 4) Chandra and XMM-Newton observations of relaxed clusters have falsified the previously accepted cooling flow model, heating mechanisms that may offset the cooling are actively being sought. 5) The superb angular resolution of Chandra is allowing us to trace a previously unknown phenomenon intimately related to the formation of galaxy clusters and of their cores. 
Silvano Molendi