Quantum many-body theory as a discipline in its own right dates largely from the 1950's. It has developed since then to its current position as one of the cornerstones of modern theoretical physics. The field remains vibrant and active, vigorous and exciting. Indeed, its successes and importance were vividly illustrated prior to the conference by the sharing of the 1998 Nobel Prizes in both Physics and Chemistry by three many-body theorists. Two of those Nobel laureates, Walter Kohn and Bob Laughlin, delivered invited lectures at this meeting, the tenth in the series of International Conferences on Recent Progress in Many-Body Theories. This series is universally recognized as being the premier series of meetings on this subject, and its proceedings have always summarized the current state of the art through the lectures of its leading practitioners. The present volume is no exception.A major aim of this conference series has been to foster the exchange of ideas between physicists working in all the diverse fields of application of quantum many-body theory. These include nuclear and subnuclear physics, quantum fluids, strongly correlated electronic systems, and low-dimensional condensed-matter systems and materials. All of these fields and others are represented in the present volume. Other topical themes covered include density functional theory and its applications to nuclear and electronic systems, quantum dots and chaos, and trapped Bose-Einstein condensates. Through this breadth of applications the reader will get a clear illustration of the power of the tools of modern microscopic quantum many-body theory, and their usefulness both in achieving a commonality of approach and understanding, and in transferring powerful ideas from one field to another.