This workshop was devoted to a discussion of recent progress made in the understanding of quantum field theories in spacetimes of less than four dimensions. In fact, the subject reached a certain degree of maturity and since most of the contributors played a major role in that progress, this volume constitutes a definitive treatise on this subject. Some of the subjects dealt with include: Quantum Groups and their Representations; W-Algebras and their Role in Physical Systems; Conformally Invariant Quantum Field Theories; Integrable Systems; Topological Field Theories.

This workshop focuses on recent developments in string theory and other related low-dimensional models.

The workshop collected together theoreticians and experimentalists for a discussion about the most recent experiments and their impact on theoretical ideas. The discussion included the new data from LEP and SLD, the evidence for the top quark from Tevatron, the structure function measurements from HERA, and the searches for dark matter. Also, new projects for physics with large neutrino detectors and CP violation at e+e- factories were presented, and a survey of high energy astroparticle physics was included. Particular attention was paid to the interplay between microscopical and cosmological scales.

An accelerating convergence of interests of particle physics and modern experimental and theoretical astrophysics has been witnessed in the past few years. One of the focal points is the observation and phenomenological characterization of Dark Matter from Galactic to the large scale structure of the Universe. Particle physics provides detailed predictions for the cosmological impact of various dark matter candidates. The other central subjects are neutrino astronomy and cosmic ray reactions which provide valuable information both on stellar structure (solar neutrinos) and on the nature of extreme high energy particle interactions. The lectures presented here represent important new contributions to all these fields.

This book addresses the theoretical aspects of the search for 'new physics' beyond the Standard Model of elementary particle interactions. Both accelerator-based and non-accelerator ('astro particle physics') searches are discussed. The contents of the Proceedings are unique in its emphasis on the interaction between these two aspects of particle physics.

The twentieth Johns Hopkins Workshop on current problems in particle theory took place in Heidelberg. The topic of the workshop was chosen in view of the phantastic success enjoyed by the standard model of electroweak and strong interactions.Until today, no significant deviations from the predictions of the standard model have been observed. However, precision tests have been dominantly performed in the high-energy domain, where the QCD coupling constant is small enough to allow for a perturbative treatment of the strong interaction. It is therefore very important to consider also the low-energy region for which non-perturbative aspects of QCD come into play.