The Interdecadal Pacific Oscillation (IPO), which can be regarded as the Pacific-wide manifestation of the Pacific Decadal Oscillation that has been described for the North Pacific, is a mode of sea surface temperature (SST) variability that provides a major source of decadal climate variability in the South West Pacific. With a change from the negative to positive phase around 1977/78, mean sea-level pressure increased west of the dateline, and decreased to the east. Changes in the characteristics of El Niņo-Southern Oscillation (ENSO) have been noted, such as the direction of propagation of the developing El Niņo warm anomaly in SST. The IPO also appears to modulate teleconnections with ENSO in a geographically-varying way. For New Zealand there is a consistent bias towards stronger ENSO-climate correlations during the positive IPO period, whereas ENSO correlations with Australian rainfall were stronger during negative IPO. Shifts in the position of the South Pacific Convergence Zone (SPCZ) also occur on the interdecadal timescale and appear to be largely linearly independent of the well-documented shifts in the SPCZ with ENSO. These aspects of the IPO as they affect southwest Pacific climate variability will be discussed, with the emphasis on insights gained from recent modeling studies.