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 was a joint meeting of the Johns Hopkins Workshop and PASCOS. It was interdisciplinary in its nature. The proceedings gives an overview of the current situation in the interrelated fields of elementary particle physics, astrophysics and cosmology as well as provides a forum for the presentation new results.

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.

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.

The physics of neutrinos has acquired a rapidly increasing role within the realm of particle physics. Recognized as an elusive particle since the prediction of its existence by Pauli and its incorporation into particle theory by Fermi in the early thirties, the neutrino was first observed some twenty years later by Reines and Cowan. Experiments carried out by Lederman, Schwartz, Steinberger et al. first revealed the existence of several species of neutrinos. By now, neutrino physics has matured to the point where detailed properties of neutrinos and their mixing can be studied by a number of experiments carried out in various high energy laboratories. Such experiments are relevant not only from viewpoint of understanding the properties of elementary particles, but also the early history of the Universe.This volume discusses the most recent experimental and theoretical results in that exciting area of particle physics.

This volume offers a comprehensive overview of our understanding of gravity at both the experimental and the theoretical level. Critical reviews by experts cover topics ranging from astrophysics (anisotropies in the cosmic microwave background, gamma ray bursts, neutron stars and astroparticles), cosmology, the status of gravitational wave sources and detectors, verification of Newton's law at short distances, the equivalence principle, gravito-magnetism, measurement theory, time machines and the foundations of Einstein's theory, to string theory and loop quantum gravity.