This book should fill a gap which has existed in the literature on supercon­ ductivity. There have been a number of excellent textbooks available on the phenomenon of superconductivity, which describe in detail the variety of ef­ fects connected with it and the mathematical techniques to deal with them properly. However, until now there has not been a textbook available in English which concentrates on the mate~ial aspects of superconductivity. This is a major shortcoming since most physicists working in the field of superconduc­ tivity are mainly concerned with specific materials and subsequently often need to know more about the interplay of superconductivity and material prop­ erties. On the other hand, people working in the field know that a competent and well-written book by S. V. Vonsovsky, V. A. Izyumov, and E. Z. Kurmaev has been available in Russian. It presents a thorough discussion of superconducting transition-metal alloys and compounds. This volume is a translation of an updated version of the Russian edition. The translation was done by A. P. Zavarnitsyn of the authors' institution and by Dr. E. H. Brandt of the Max-Planck-Institut fur Metallforschung in Stuttgart. The master manuscript was ably typed by Mrs. C. Pendl. I would like to take this opportunity to thank each of them. I sincerely hope that the book will turn out to be useful to physicists working in the field of superconductivity as well as to nonspecialists and interested graduate students.