During the last decade, various powerful experimental tools have been developed, such as small angle X-ray and neutron scattering, X-ray and neutron reflection from interfaces, neutron spin-echo spectroscopy and quasi-elastic multiple light scattering and large scale computer simulations. Due to the rapid progress brought about by these techniques, one witnesses a resurgence of interest in the physicochemical properties of colloids, surfactants and macromolecules in solution. Although these disciplines have a long history, they are at present rapidly transforming into a new, interdisciplinary research area generally known as complex liquids or soft condensed matter physics: names that reflect the considerable involvement of the chemical and condensed matter physicists. This book is based on lectures given at a NATO ASI held in the summer of 1991 and discusses these new developments, both in theory and experiment. It constitutes the most up-to-date and comprehensive summary of the entire field.