The western Pacific warm pool (WPWP) is a region of highest oceanic temperature in the world, gathers huge heat, and plays a very important role in the climate system of the earth. This paper reviews progresses in the WPWP study during the past 30 years, including the mechanism underlying the formation of WPWP, multi-scale variability and corresponding physical causes, and progresses in observation and numerical simulation of the WPWP. The WPWP formation is thought to be a result of coupled atmospheric and oceanic processes in the context of modern topography. Strong variability of the WPWP can be detected on time scales from intra-seasonal to century time scales. Thereinto, the mechanism of the intra-seasonal variability includes variability in convection and sea surface heat flux associated with the Madden Julian Oscillation and ocean dynamics like oceanic waves. WPWP seasonality is mainly induced by the seasonal fluctuation in solar radiation. On an inter-annual time scale, the WPWP plays as a part of the El Ni?o-Southern Oscillation cycle and hence shows significant interannual variability. The Pacific Decadal Oscillation and Atlantic Multi-decadal Oscillation derive the inter-decadal variability of the WPWP, while on a century time scale, the WPWP shows an extending trend under the global warming. Systematical observation of the WPWP started from the application of ocean satellites, and then several observational projects including WCRP/TOGA, TAO/TRITON, TOGA-COARE, WOCE, Argo, SPICE and NPOCE were lunched successively, which have significantly promoted the WPWP study. But until the recent Coupled Model Intercomparison Project 5, most of the climate models failed to exclude the tropical SST bias, and simulation of the WPWP is not good enough yet, indicating a long way to better understand the WPWP dynamics and simulate the observed WPWP.