Empirical evidence is presented to support a hypothesis that the interdecadal variation of the Indian summer monsoon and that of the tropical SST are parts of a tropical coupled ocean–atmosphere mode. The interdecadal variation of the Indian monsoon rainfall (IMR) is strongly correlated with the interdecadal variations of various indices of El Niño–Southern Oscillation (ENSO). It is also shown that the interannual variances of both IMR and ENSO indices vary in phase and follow a common interdecadal variation. However, the correlation between IMR and eastern Pacific SST or between IMR and Southern Oscillation index (SOI) on the interannual timescale does not follow the interdecadal oscillation. The spatial patterns of SST and sea level pressure (SLP) associated with the interdecadal variation of IMR are nearly identical to those associated with the interdecadal variations of ENSO indices. As has been shown earlier in the case of ENSO, the global patterns associated with the interdecadal and intera... Abstract Empirical evidence is presented to support a hypothesis that the interdecadal variation of the Indian summer monsoon and that of the tropical SST are parts of a tropical coupled ocean–atmosphere mode. The interdecadal variation of the Indian monsoon rainfall (IMR) is strongly correlated with the interdecadal variations of various indices of El Niño–Southern Oscillation (ENSO). It is also shown that the interannual variances of both IMR and ENSO indices vary in phase and follow a common interdecadal variation. However, the correlation between IMR and eastern Pacific SST or between IMR and Southern Oscillation index (SOI) on the interannual timescale does not follow the interdecadal oscillation. The spatial patterns of SST and sea level pressure (SLP) associated with the interdecadal variation of IMR are nearly identical to those associated with the interdecadal variations of ENSO indices. As has been shown earlier in the case of ENSO, the global patterns associated with the interdecadal and intera...