The seasonal and interannual variabilities of warm pool properties in the Pacific and Indian Ocean sectors are examined and contrasted. The properties examined are the size, mean and maximum sea surface temperatures (SSTs), and central position. The seasonal variability is more vigorous in the Indian Ocean sector, but the interannual variability is comparable in the Pacific and Indian Ocean sectors. The variability is associated with significant longitudinal and latitudinal displacements on seasonal time scales but only with longitudinal displacements on interannual time scales. As for the controlling factors, while the seasonal variability of the warm pool is controlled by the annual march of the Sun in the Pacific sector and by the Indian summer monsoon in the Indian Ocean sector, the interannual variability in both sectors is related mostly to El Niño–Southern Oscillation (ENSO). ENSO is closely correlated with the size variations and longitudinal displacements of the warm pool. Interestingly, the warm pool intensity in both sectors is not highly correlated with ENSO until 5 to 6 months after ENSO peaks. The possible causes of this delayed ENSO influence are discussed. Only size and intensity (i.e., mean SST) variations in the Indian Ocean warm pool are significantly correlated with quasi-biennial variability in the Indian monsoon, which indicates that the Indian Ocean warm pool may be a potential predictor for Indian monsoon variations.