This paper presents an overview of regional climate and spatial and temporal aspects of climate variability in eastern Africa. Causal mechanisms of climate variability are also considered. In general, widely diverse climates, ranging from desert to forest, exist over a relatively small area. Rainfall seasonality is quite complex, changing within tens of kilometers. Despite this diversity, interannual fluctuations of rainfall are markedly uniform over the region and appear to be governed by the same factors. In much of the region the annual cycle of rainfall is bimodal, with a main rainy season in March-to-May and “short rains” of October–November. The main rains are less variable, so that interannual variability is related primarily to fluctuations in the short rains. These are also linked more closely to large-scale, as opposed to local, atmospheric and oceanic factors. Rainfall fluctuations show strong links to the El Nino-Southern Oscillation (ENSO) phenomenon, with rainfall tending to be above average during ENSO years. The relationship appears to be indirect, however. The main causal mechanisms appear to be fluctuations in sea-surface temperatures in the tropical Atlantic and Indian Oceans, which in turn are loosely coupled to ENSO. For the region as a whole, the Atlantic seems to affect rainfall more than the Indian Ocean.