JOHN M. WALLACE was born in New York in 1940. He received his Bachelor's degree from Webb Institute of Naval Architecture and his PhD from MIT, where he worked closely with Professors Victor P. Starr and Reginald E. Newell. He has been a member of the faculty of the Department of Atmospheric Sciences at the University of Washington since 1966. He has served terms as department chair, as Director of the Joint Institute of the Study of the Atmosphere and Ocean, and as Co-director of the University of Washington's Program on the Environment. His research interests include large scale atmospheric dynamics and climate variability and change. He regularly teaches an introductory graduate class in which this textbook is used. PETER V. HOBBS was born in London in 1936. He received his doctorate from Imperial College, University of London, where he worked in the research group headed by Sir B. John Mason. He joined the Department of Atmospheric Sciences at the University of Washington in 1963, and served as a faculty member there until his death in 2005. In his role as founder and director of the the Cloud and Aerosol Research Group(CARG) in the department, he acquired and maintained a series of instrumented research aircraft with which he and his staff and students made field measurements of clouds, frontal systems and effluents from fires, volcanoes and industrial sources in many different parts of the world. He was a prolific writer and a devoted instructor and mentor of students. In recognition of his research and teaching contributions he was named an Honorary Member of the American Meteorological Society.