This is the second Fermi School devoted to the astrophysics of galaxy clusters, held 4 years after the School “Background Microwave Radiation and Intracluster Cosmology”, directed by Professor Francesco Melchiorri and one of us (YR). The motivation for this School was provided by significant expansion in research on these largest gravitationally bound systems, and great interest in multi-faceted observational, theoretical, and numerical simulations of clusters.

Key topics in the astrophysics of clusters were covered in a series of ten pedagogical (multi-lecture) reviews; the program included also some eight seminar talks. Written versions of most of the reviews and seminar talks are included in this volume. Even though the preparation of this volume was delayed by late submission of some of the reviews, we believe that the papers included here still provide a very useful and updated account of key aspects of a wide range of topics in cluster research.

The School was attended by a substantial group of research students and senior scientists. Participants benefited from ample opportunities for informal interaction in the very enjoyable and aesthetically pleasing Villa Monastero and other locations in Varenna.

We dedicate this volume to the memory of our esteemed colleague Professor Francesco Melchiorri, a leader in experimental CMB research and a mentor to many.

Y. Rephaeli and A. Cavaliere