The papers contained in this volume are invited lec­ tures presented at the 21st "Universit~tswochen fUr Kern­ physik" in Schladming in February 1982. To consider electro­ magnetic and weak interactions as manifestations of a single theory is a standpoint, which is generally accepted by now. The goal of the school was to outline the present state of this unified theory and to discuss possible future developments. Thanks to the generous support provided by the Austrian Ministry of Science and Research, the Styrian Government and other sponsors, it was again possible to invite experts in the field as lecturers. The lecture notes have been reexamined by the authors and are now published in their final form to enable a larger number of physicists to profit from them. Since the lectures are already quite voluminous, we have decided to restrict the publication to the lectures themselves and omit all seminars, interesting as they were, as well as all details connected with the meeting. It is a pleasure to thank all the lecturers for their efforts, making it possible to speed up publication. Thanks are also due to L. Pittner for organisation and proof-reading as well as to Mrs. Krenn and Mrs. Neuhold for the careful typing of the papers. H. Mitter Acta Physica Austriaca, Suppl. XXIV, 3-62 (1982) © by Springer-Verlag 1982 INTRODUCTION TO GAUGE THEORIES OF ELECTRO­ + WEAK INTERACTIONS by G. ECKER Institut fUr Theoretische Physik Universitat Wien, Austria TABLE OF CONTENTS I.