Tropical atmosphere and ocean are receiving increased attention in relation to the functioning of the global climate system, the remarkable climatic variability in low latitudes, and the associated manifold environmental and societal consequences. Beyond the traditional emphasis of meteor ology on weather analysis and forecasting, there is a growing interest in the climate and large scale circulation of the tropics. This book may serve as a text for graduate and upper-division undergraduate students in meteorology, and is also intended as a reference work for practicing meteorologists, and researchers in the atmospheric, oceanic, and other environmental sciences. I began writing this book in 1979, but the roots reach further back. Early experiences in North Africa fuelled my curiosity about the low latitudes. In 1960 I seized the opportunity to work in the National Meteorological Service of El Salvador in Central America. My interest in the tropics continued after joining the University of Wisconsin in 1963. Field research brought me to the equatorial Pacific, and many times to the tropical Americas and Africa. This involved visits and correspondence with many weather services. My acquaintance with Australasia and South Asia is limited to short study visits, but includes continuous contacts with colleagues at key research institutions in India, namely the India Meteorological Department, the Indian Institute of Tropical Meteorology, and Andhra University. A guest semester at the University of the Witwatersrand in 1971 and related travels provided a perspective on the problems of Southern Africa.