Astrophysicists and astronomers have succeeded in formulating a consistent picture of the expanding universe that rests on highly symmetric solutions of Einstein?s theory of gravitation coupled to a single matter model. This model seems to be valid from a fraction of a second after the big bang up to the present epoch, and it explains the synthesis of the light nuclei, the existence and properties of the microwave background, as well as the global average properties of matter distribution. It also allows the accommodation of such global phenomena as the overall expansion of the system of galaxies, the number counts of celestial objects, the evolutionary effects in quasars and radio galaxies, as well as the fact that the age information obtained from meteorites, minerals, and stars agrees well with the expansion rate. This "standard model" actually includes a wide range of possible cosmological models, which differ in the values of various ? in principle, measurable ? parameters (e.g., the expansion velocity, the deceleration of the galaxy system, the mean density of matter and radiation, etc.), but which share some basic properties. Cosmological models describe a world that expands from a hot big bang that is globally homogeneous, isotropic, and in a thermochemical equilibrium, and which has developed inhomogeneous structures, e.g., galaxies from initial small-density fluctuations through gravitational instability. This volume is the record of intense discussions between physicists, astronomers, and astrophysicists. It focuses on four main issues: How do galaxies form? How well do we understand the formation of large-scale structures? What is the relation between cosmology and fundamental theories of particle physics? What do we know about the global properties of the universe? Among the topics illuminated from various perspectives are the nature and distribution of dark matter in the universe, the possible discrepancy in recent astronomical data between the age and the expansion time of the universe, and speculations about the very early universe. This volume provides not only an in-depth status report on cosmology, but also defines areas where progress is to be-expected in the near future. Goal of this Dahlem Workshop: to examine conceptual, theoretical, and observational problems of the formation of structure in the universe.