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.

From 31 July to 11 August 1981, a group of 108 physicists from 75 laboratories in 27 countries met in Erice for the 19th Course of the International School of Subnuclear Physics. The countries re presented were Argentina, Australia, Austria, Belgium, Brazil, Bulgaria, Canada, Denmark, the Federal Republic of Germany, Finland, France, Greece, Hungary, India, Israel, Italy, Japan, Korea, the Netherlands, Norway, Poland, Sweden, Turkey, the United Kingdom, the United States of America, Venezuela, and Yugoslavia. The School was sponsored by the Italian Ministry of Public Education (MPI), the Italian Ministry of Scientific and Technological Research (MRST) , the Regional Sicilian Government (ERS), and the Weizmann Institute of Science. The programme of the School was mainly devoted to a review of the most significant results, both in theory and experiment, obtained in the field of high-energy interactions. The outcome of the School was to present a clear picture of how far we are along the fascina ting route towards understanding the deep meaning of the natural laws of hadronic and leptonic matter -- the final goal being the unity of all forces.