This book lays out a science plan for a major, international, 15-year research program. The past 10 years have seen significant progress in studies of short-term climate variations, in particular for the region of the tropical Pacific Ocean and the El Nino/Southern Oscillation phenomenon. Some forecast skill with lead times as long as a year in advance has already been developed and put to use. The GOALS program plans to capitalize on this progress by expanding efforts on observations and seasonal-to-interannual predictions to the remainder of the tropics and to higher latitudes.