The interval from the middle Eocene to early Oligocene represents one of the most significant transitions in Earth’s climate, during which greenhouse conditions were supplanted by icehouse conditions of the present day. This global transition was preceded by a long-term cooling phase and short-term uncorrelated variations in several marine proxies, which indicate paleoceanographic instabilities prior to the key climatic transition. We integrate previous multidisciplinary studies with recent data from the Massignano section (Umbria-Marche Basin) and summarize interpretations of studies from the past 20 yr that have been based on the Eocene-Oligocene boundary global stratotype section and point (GSSP). Based on...