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...