This chapter reviews critical sequences of Late Eocene limestones in the Indo-West Pacific region to establish the nature of the faunal change at the Eocene–Oligocene boundary and of linking it with any geological features of regional importance that may be apparent from the successions themselves. Eocene and Oligocene limestones are numerous in the Indo-West Pacific region and a great deal is known about their faunas. There is, however, little published information on the boundary itself, and only at Melinau, Sarawak, have Eocene and Oligocene limestones been found at outcrop in an apparently unbroken sequence. The major change that everywhere affected larger foraminifera at or toward the end of Eocene times seems to have been marked by a distinct depositional hiatus in most areas of shallow-water carbonate sedimentation. The cause could have been a global fall in sea level that exposed many inner shelf carbonates to erosion. © 1986, Elsevier Science & Technology