This book contains the lectures presented at the Summer Advanced Study Institute, 'Physics and Chemistry of Atmospheres' which was held at the University of Liege, Belgium, during the period July 29-August 9, 1974. One-hundred nineteen persons from eleven different countries attended the Institute. The authors and publisher have made a special effort for rapid publication of an up to-date status of the physics and chemistry ofthe atmospheres of Earth and the plan ets, which is an ever-changing area. Special thanks are due to the lecturers for their diligent preparation and excellent presentations. The individual lectures and the published papers were deliberately limited; the authors' cooperation in conforming to these specifications is greatly appreciated. The contents of the book are organized by subject area rather than in the order in which papers were presented during the Institute. Many thanks are due to Drs Alv Egeland, Donald M. Hunten, Gunther Lange-Hesse, Marcel Nicolet, Harold I. Schiff, Lance Thomas, Alister Vallance Jones, Richard Wayne, and Gilbert Weill who served as session chairmen during the Institute and contributed greatly to its success by skillfully directing the discussion period in a stimulating manner after each lecture. Many persons contributed to the success of the Institute. Drs Alv Egeland, Donald M. Hunten, Gunther Lange-Hesse, Marcel Nicolet, Harold I. Schiff, Erwin R. Schmerling, Lance Thomas, Alister Vallance Jones, Richard Wayne, and Gilbert Weill were especially helpful in preparing the technical program.