The Eocene—Oligocene climate transition (EOCT) was a period of rapid global cooling at abou 34 Ma ago, representing a major step from early Cenozoic greenhouse toward modern icehouse conditions. It was accompanied by a series of dramatic changes in Earth's environmental system, including an expansion of ice sheets on the Antarctic continent, a global sealevel drop, a declining atmospheric CO2 concentration, a deepening of the calcite compensation depth, and a biotic reorganization, thus has great significance in understanding the mechanisms behind the longterm Cenozoic cooling, the behavior of regional climate in response to rapid cooling and the effects of major climatic changes on the biotic reorganization. This review summarizes recent progress in studying EOCT. (1) Significant cooling during this transition inferred from geological records of different latitudes indicates this phenomenon was triggered by global rather than regional factors. (2) The declining of atmospheric CO2 and the associated global carbon cycle changes have been proved as the primary causes of EOCT by modeling studies, rather than the previous hypothesis that the Antarctica was thermally isolated by the initiation of Antarctic Circumpolar Current. (3) Marine records revealed that this transition is marked by a twostep increase of benthic foraminiferal oxygen isotope values occurred within 400~500 ka, reflecting the drop of global temperature and establishment of Antarctic ice sheets, respectively. (4) A comparison of the EOCT interval in Asian terrestrial records with marine records suggests that the regional aridification mainly corresponds to atmospheric cooling (i.e., the first step of EOCT) rather than ice volume growth. However, there are still many questions remained unsolved. Future application of more detailed and accurate proxies of atmospheric CO2 and paleotemperature, recovery of highresolution sediment archives from the oceans and continents and more complex models across the EOCT will further reveal the changes of each environmental factor during this transition and their relationship with each other, and obtain a thorough understanding of the mechanisms behind this critical climate transition.