The subterranean environment of Christmas Island is diverse and includes freshwater, marine, anchialine, and terrestrial habitats. The cave fauna comprises swiftlets, and a diverse assemblage of invertebrates, both terrestrial and aquatic, which includes a number of rare and endemic species of high conservation signicance. At least twelve species are probably restricted to subterranean habitats and are endemic to Christmas Island. Previously poorly known, the cave fauna of Christmas Island is a signicant component of the island's biodiversity, and a signicant cave fauna province in an international context. The cave fauna and habitats are sensitive to disturbance from a number of threatening processes, including pollution, deforestation, mining, feral species and human visitors.