With the advent of heavy-ion reactions, nuclear physics has acquired a new frontier. The new heavy-ion sources operating at electrostatic accelerators and the high-energy experiments performed at Berkeley, Dubna, Manchester and Orsay, have opened up the field, and have shown us impressive new prospects. The new accelerators now under construction at Berlin, Daresbury and Darmstadt, as well as those under consideration (GANIL, Oak Ridge, etc. ) are expected to add significantly to our knowledge and understanding of nuclear properties. This applies not only to such exotic topics as the existence and lifetimes of superheavy elements, or the possibil ity of shock waves in nuclei, but also to such more mundane issues as high-spin states, new regions of deformed nuclei and friction forces. The field promises not only to produce a rich variety of interesting phenomena, but also to have wide-spread theoretical implications. Heavy-ion reactions are characterized by the large masses of the fragments, as well as the high total energy and the large total angular momentum typically involved in the collision. A purely quantum-mechanical description of such a collision process may be too complicated to be either possible or inter esting. We expect and, in some cases,know that the classical limit, the limit of geometrical optics, a quantum-statistical or a hydrodynamical description correctly account for typical features.

A NATO Advanced Studies Institute was held June 12-23, 1978, at the University of Wisconsin in Madison, Wisconsin. It was a topical Institute in theoretical nuclear physics and had the some what novel feature of focussing not on a single topic but on two closely allied ones: pion-nucleus and heavy-ion physics. These two fields. both dedicated to the investigation of short-wave length properties of nuclei, have many techniques and concepts in cornmon, and essentially become one in the topic of relativistic heavy-ion physics. The purpose of including both in a single Institute was to encourage the practitioners in each of these fields to learn from those in the other; to judge from the liveli ness of the questioning which ensued, the purpose was well-served indeed. Because the Institute was viewed as one which served both educational and research ends, the lecturers took particular pains to develop their subjects in a careful, coherent sequence. The result is a compendium of advanced techniques and current results in these two rapidly-expanding fields of nuclear theory which should serve interested physicists as an ideal introduction to the fields. In addition to the support provided by the Scientific Affairs Division of NATO, substantial financial assistance was provided by the U. S. National Science Foundation and the Graduate School of the University of Wisconsin.