In this review of the Southern Oscillation we consider oceanic and atmospheric circulation changes and related rainfall anomalies with special emphasis on the region of South America. The climate anomalies associated with Southern Oscillation—El Niño (ENSO) events are highly persistent and nearly global in extent. The persistent nature of these events derives from strong coupling between atmosphere and ocean. Although the initial causes of the oscillation are unclear, once initiated the Southern Oscillation (SO)follows a certain sequence of events with well-defined effects on rainfall over a large portion of the tropics and subtropics. Drought in Australia, Indonesia, India, West Africa and Northeast Brazil as well as excessive rainfall in the central and eastern Pacific, Peru, Ecuador and Southern Brazil are all related to the SO. ENSO events are also associated with dramatic changes in the tropospheric flow pattern over a broad area of both hemispheres. Wintertime upper tropospheric subtropical jets are especially pronounced as are changes in the low level trade wind regime of both the South Pacific and South Atlantic Oceans. Mid-latitude blocking patterns are also more frequent in certain regions during ENSO events.