This volume contains the written versions of the lectures held at the 22 Internationale Universitatswochen fur Kern- physik in Schladming, Austria, in February 1983. The generous support of the Austrian Federal Ministry of Science and Research, the Styrian Government and other sponsors once again made it possible for expert lecturers to be invited. In choosing the topics, the aim was to achieve a balance between the theoretical and phenomenological contributions; on the theoretical side, discussions centred on the impact of different approaches to quantum field theory on the ele- mentary...