Work on the unification of the fundamental particle interac tions has continued vigorously since the first Europhysics study Conference on this subject. At that time we emphasized the exis tence of two main approaches, one based on supersymmetry and pos sibly its local version, supergravity, and the other approach based on grand unified gauge theories. Discussion of the possible tests of these theoretical speculations included experiments on baryon decay and neutrino oscillations. In view of the uncertainties surrounding the observability of such phenomena, the early Universe was welcomed as a possible Laboratory for testing new theoretical ideas. At that time, we expressed the hope that the different gauge and super symmetry approaches would cross-fertilize each other" and it is appropriate to ask now how much of that hope has been realized. We believe there has recently been considerable theoretical rapprochement, which is amply reflected in these Proceedings. On the one hand it has been realized that many of the technical pro blems in grand unified gauge theories, such as arranging the hierarchy of different mass scales, may be alleviated using simple global supersymmetry. On the other hand there has been growing interest in the possibility that extended supergravity theories may furnish a suitable framework for the unification of all the fundamental particle interactions. Many physicists in fact now question actively whether the known "fundamental" particles are in deed elementary, or whether they are composite.

This volume constitutes the Proceedings of a Europhysics Study Conference held in Erice, Sicily from March 17 to 24, 1980. The objective of the meeting was to bring together practitioners of two different approaches to the unification of the fundamental par ticle interactions: supersymmetry and supergravity on the one hand, and grand unified gauge theories on the other hand. The hope was that exposure to each others' ideas and problems would at least aid mutual comprehension, and might start people thinking how to develop a synthesis of the two approaches which could avoid their individual shortcomings. It is not clear to us how successful the conference was in achieving these objectives. On the one hand many important ad vances in supersymmetric theories were reported which were primarily of a technical nature, while some interesting attempts to probe the phenomenological consequences of supersymmetry and supergravity were also presented. On the other hand there was considerable in terest in phenomenological aspects of grand unified theories such as proton decay, neutrino masses and oscillations, and links with cosmology. There was also some work on model-building but rela tively few purely technical advances. A few speakers tried to build bridges between the formalism of supersymmetry or supergravity and the phenomenologically successful gauge theories of elementary par ticle interactions.

The theoretical understanding of elementary particle interactions has under gone a revolutionary change during the past one and a half decades. The spontaneously broken gauge theories, which in the 1970s emerged as a prime candidate for the description of electro-weak (as weIl as strong) interactions, have been confirmed by the discovery of neutral weak currents as weIl as the w- and Z-bosons. We now have a field theory of electro-weak interactions at energy scales below 100 GeV-the Glashow-Weinberg-Salam theory. It is a renormalizable theory which enables us to do calculations without en countering unnecessary divergences. The burning question now is: Wh at lies ahead at the next level of unification? As we head into the era of supercolliders and ultrahigh energy machines to answer this question, many ap, pealing possi bilities exist: left-right symmetry, technicolor, compositeness, grand unifica ti on, supersymmetry, supergravity, Kaluza-Klein models, and most recently superstrings that even unify gravity along with other interactions. Experi ments will decide if any one or any combination of these is to be relevant in the description of physics at the higher energies. As an outcome of our con fidence in the possible scenerios for elementary particle physics, we have seen our understanding of the early uni verse improve significantly.

For the Galvani Bicentenary Celebrations, the University of Bologna and its Academy of Sciences singled out subnuclear physics as the field of scientific research to be associated with this important event, as it would best illustrate, for the new generation of students, the challenge inherent in fundamental sciences. Subnuclear physics has represented, ever since it was born, the new frontiers of Galilean science. In his opening lecture delivered on the first day of the new academic year, Professor Antonino Zichichi analytically reviewed the basic conceptual developments and main discoveries achieved in subnuclear physics since its birth in the 20th century. Given the importance of this field of fundamental research, Professor Zichichi was invited to expand the contents of his lecture into a book, and the outcome is this volume.

For almost two decades Prof. Shifman, a clear and pedagogical expositor, has been giving review lectures on frontier topics in theoretical high energy physics. This two-volume book is a collection of some of the best of those lectures. The lectures written in the 1980's and early 1990's have been revised and updated specifically for this publication. The lectures in this book are intended for beginners - graduate students and young researchers - who are about to delve into the intricacies of the theory. They were used by the author in his course ';Advanced Modern Field Theory and Its Applications';, given in the academic year 1994/95 at the University of Minnesota.A wide range of key topics is covered. In Volume 1, the first two chapters are devoted to quantum chromodynamics as the theory of hadrons. The author gives an in-depth discussion of a variety ofpowerful methods based on Wilson's operator product expansion. Chapter 3 (written together with V Novikov, A Vainshtein, and V Zakharov) is the most systematic and pedagogical presentation of instantons in the gauge theories one can find in the literature. Chapter 4 introduces supersymmetry. Chapter 5, concluding this volume, reviews the fascinating dynamics of supersymmetric gauge theories in the strong coupling regime. Chapter 6, which opens Volume 2, is a culmination of the supersymmetric theme. It gives a state-of-the-art description of the breakthrough developments in supersymmetric gauge theories. It has been written specifically for this book by A Vainshtein and the author. Chapter 7 is designed as a primer of two-dimensional conformal field theory, which constitutes the basis of modern string theory. Chapter 8, the last, presents remarkable new findings in quantum mechanics. Every chapter contains exercises and a list of recommended literature.Prof. Shifman has been an active participant and significant contributor in the development of the ideas presented in this book. This accounts for the historical remarks and digressions interspersed in the book, enhancing its pedagogical role. The book will serve as a comprehensive reference and textbook for all graduate students and researchers interested in modern particle physics. It will also be a useful guide for lecturers.