The potential for finding Quaternary tetrapod fossils on islands is governed by a combination of biodiversity, geology, fossil preservation, and time span of records. Islands with extensive limestone exposures are particularly well represented at low and middle latitudes, where biodiversity is potentially high, and the caves and karst fissures in these landscapes have proven to be rich reliquaries of the Quaternary fossil record. This is particularly apparent when we contrast limestone islands with volcanic islands in the Lesser Antilles; the latter present a serious deficiency in the fossil vertebrate record and an impediment to understanding the biogeography of the region. Caves and karst fissures are also ephemeral on geological time scales, and few tropical island sites are known that are older than the Last Interglacial. In Britain, important cave sites of Middle Pleistocene age are known, but are rare.