The Late Eocene and the Eocene-Oligocene (E-O) transition mark the most profound oceanographic and climatic changes of the past 50 million years of Earth history, with cooling beginning in the middle Eocene and culminating in the major earliest Oligocene Oi-1 isotopic event. The Late Eocene is characterized by an accelerated global cooling, with a sharp temperature drop near the E-O boundary, and significant stepwise floral and faunal turnovers. These global climate changes are commonly attributed to the expansion of the Antarctic ice cap following its gradual isolation from other continental masses. However, multiple extraterrestrial bolide impacts, possibly related to a comet shower that lasted more than 2 million years, may have played an important role in deteriorating the global climate at that time. This book provides an up-to-date review of what happened on Earth at the end of the Eocene Epoch.