Spatial and temporal characteristics of the Indian Ocean Dipole (IOD) and the relationship between the variabilities of IOD and ENSO at several interannual time scales are addressed. It is found that the interannual variability of IOD is associated with that of ENSO significantly at the time scales of quasi-1—2 years, quasi-3 years, and quasi-4 years. Besides, IOD also exhibits a robust variation at the quasi-8-month time scale which appears to be independent on the ENSO. At the three interannual time scales mentioned above, the IOD contributes to the interannual variations of ENSO through the westward shifts of zonal wind anomalies associated with the IOD over the tropical Indian Ocean into the tropical Pacific Ocean. The similar process is not found for the quasi-8-month mode of IOD. In addition, the ocean-atmosphere interactions in the tropical Indian Ocean responsible for the interannual variations of IOD are different at the four different time scales.