Due to extensive morphological variation and inadequately-sampled or poorly-designed studies, the taxonomy of the finless porpoises (genus Neophocaena) has been controversial for some time. An uneasy stability with the arrangement of finless porpoises into a single species consisting of three subspecies dominated for many years. However, in the past decade new data examining both morphological and molecular characters provided strong evidence for the existence of at least two distinct biological species, by demonstrating a lack of interbreeding in sympatry between the two major morphological forms of finless porpoises. All finless porpoise specimens examined have had either a wide dorsal tubercled area or a much-narrower one, and there appears to be no overlap between the two species in this feature. Furthermore, the two species have apparently been reproductively isolated since the last glacial maximum, about 18,000 years ago. Taxonomic studies of finless porpoises are reviewed, the widely-accepted view of one species is rejected, and the two recognized species are redescribed. The revised taxonomy of the finless porpoises includes the Indo-Pacific finless porpoise (Neophocaena phocaenoides) and the narrow-ridged finless porpoise (N. asiaeorientalis), with two subspecies (Yangtze finless porpoise, N. a. asiaeorientalis, and East Asian finless porpoise, N. a. sunameri) within the latter species.