Nomascus leucogenys (Ogilby, 1840) is a crested gibbon of northern Vietnam, northern Laos, and southern China. Males are black with white cheeks and females are a rich buff color with a dark brown sagittal crest. It is among the largest of hylobatids (except siamang) and has unusually long arms for a hylobatid. Its diet includes fruits, leaves, small animals, and flowers. It is territorial and lives with stable pair-bonds in nuclear families consisting of a male and female and their offspring. It is “Critically Endangered,” possibly extirpated from China with only isolated populations remaining in Laos and Vietnam.