The Indian Ocean is often thought of as an ocean that responds in a predictable manner to a very strong annual cycle imposed by the monsoons and the ENSO cycle. Evidence of interannual variability has been found that suggests that there is a biennial variability in the Indian Ocean region (Meehl, Yasunari). In addition, and occasionally, sometimes through the influence of an El Nino, but sometimes independently, large scale excursions from the annual cycle occur producing El Nino-like variability within the Indian Ocean. The years 1961–62 and 1997–98 were such years. In fact, during the fall of 1987 and 1998 the greatest warming of the century has occurred in the western Indian Ocean. This warming is superimposed on a general warming trend that has placed the equatorial Indian Ocean in its warmest state in the last 100 years. Anomalous surface easterly winds, the near-equatorial sea surface temperature gradient and the slope of the ocean surface reversed itself for a prolonged period with warmer temperatures (+ 3&C) and an elevated surface (+30 cm) in the west and cooler temperatures (-3C) and depressed sea levels (-30 cm) in the east. It is hypothesized that the different signatures associated with this El Nino (e.g., normalrainfall in Indian and Australia, instead of droughts and 100-year rainfalls in East Africa, instead of somewhat above average rainfall) were associated with the anomalous Indian Ocean. The signatures of the anomalies were so strong in the Indian Ocean that interactive ocean-atmosphere modes are relatively easy to identify. The identification is made, and the morphology followed, using a combination of satellite OLR, SST and altimetry data as well as reanalysis data. The role that these modes play in the biennial variability of the monsoon is discussed. Finally, the issue of the long-term trend in the SST and what this might mean in terms of future interannual variability of the monsoon is identified as a pressing problem