Great progresses have been made in understanding, modeling, and predicting the basic features of the El Nino-southern Oscillation (ENSO) phenomenon characterized by interannual warming/cooling of the central to eastern equatorial Pacific and weakening/strengthening of tropical Pacific trade winds. ENSO's intensities, durations, patterns of sea surface temperature anomalies vary substantially from event to event. These differences often have significant global consequences. Climate models still exhibit large spread in simulating ENSO’s time-space complexities. Better simulations and predictions of ENSO require a deeper understanding of its diversity. What are the main causes for the apparently different patterns and durations of ENSO as perceived from different ENSO types? What are the roles of the annual cycle and ENSO interaction and other multi-scale nonlinear interaction in ENSO diversity? This talk will briefly highlight some recent progresses in addressing these issues.