Professor Francesco Melchiorri and I organized and directed the first international school devoted to the study of the Sunyaev-Zeldovich (S-Z) effect, and important related topics in cluster and CMB research. Francesco died on Thursday, July 28, 2005; he will be greatly missed by his many students, friends, and colleagues! This volume is dedicated to his memory.

Francesco Melchiorri was a pioneer and a champion of experimental cosmology in Italy. He began experimental and observational work on the CMB more than 30 years ago. The work he and his colleagues have carried out resulted in major contributions to CMB measurements in general, and CMB anisotropy in particular. Francesco’s scientific leadershipemanated in a gentle, unassuming style and was based on his scientific vision and mastery of the field and its experimental complexities. He maintained a high level of involvement in experimental CMB research, supervised the work of a large number of students, and was the mentor to the many researchers in his dynamic group. The groupactivities in recent years included a significant involvement in experimental and observational S-Z work with the MITO telescope.

This “Enrico Fermi” Summer School on the S-Z effect and closely related research topics was held after extensive theoretical and observational work was done following the seminal work of Sunyaev and Zeldovich in the 1970s, and just ahead of a major leap forward in the very near future when thousands of clusters will be detected by a large number of CMB and dedicated S-Z projects. Most of these are new bolometer arrays with high spatial resolution and multi-spectral capabilities. S-Z science is about to be significantly enhanced by unique, multi-faceted cluster and cosmological yield, at a level of precision in accord with the high standards of the current era that was heralded by spectacular achievements in cosmological CMB research.

The pedagogical reviews and technical seminars included in this volume represent most of the important current topics in S-Z work and in the astrophysics of clusters. For the large groupof research students and many senior scientists who attended the School, this was an excellent opportunity for comprehensive exposition to all relevant aspects of the the S-Z effect and its use as a precise cluster and cosmological probe. The relaxed pace of the School, the ample opportunity for informal interaction between all participants, and the elegant physical environment of Villa Monastero in the beautiful Varenna setting, have all contributed significantly to the success of the School.

To commemorate the 40th anniversary of the detection of the CMB by Penzias and Wilson (in 1964), we held a special session devoted to the history of this discovery. In his fascinating account of their work, Arno Penzias outlines also some lessons pertinent to current scientific issues. In other talks in this session very interesting related observational work in Europe and the US is reviewed.

Finally, the School program included several additional talks by Rachel Bean, Paolo de Bernardis, Jean-Michel Lamarre, Yoel Rephaeli (on nonthermal phenomena in clusters), and Rashid Sunyaev. Unfortunately, written versions of these talks were not provided due (mostly) to time constraints.

Y. REPHAELI