The theory of simple and complex fluids has made considerable recent progress due to the emergence of new concepts and theoretical tools, the availability of a large body of new experimental data on increasingly complex systems, and far-reaching developments in numerical simulation. Two clear trends emerge from the present book: first, the diversity of new and unexpected theoretical results relating to classical models of liquids; and secondly, the parallel emergence of new concepts, models and methods for the investigation of complex fluids and phenomena. The book lays stress on a tutorial presentation of the main topics, including liquid structure, metastability and phase transitions, confined fluids and interfaces, complex fluids and quantum fluids. Audience: Physicists, physical chemists, materials scientists and engineers who require an up-to-date account of recent progress in a rapidly growing, interdisciplinary area. Graduate students who need and introduction to the novel concepts and methods in the field.