The physics of phonons is a rapidly growing branch of solid state physics. In the present volume A.A. Maradudin presents a thorough review of its current development. This is followed by papers from international specialists studying a variety of theoretical and experimental problems: The foundations of the dynamics of condensed media, including surface vibrations and localization of phonons: phonon kinetics and phonon spectroscopy; and finally the interaction of phonons and electrons. The lectures address graduate students as well as specialists because the main purpose of this publication is to give an overview of the present development of phonon physics.