Crested gibbons Nomascus spp are the rarest genus of the family Hylobatidae, and the Hainan gibbon Nomascus hainanus is the rarest primate in the world, numbering around 20 individuals. The Eastern black gibbon Nomascus nasutus, also known as Cao Vit gibbon, numbers <110 individuals in their native habitat. Both gibbon species are Critically Endangered and neither of these species is maintained in captivity. Conservation efforts for these species are currently under way. However, there is an urgent need for additional surveys, reforestation programmes, increased educational outreach to people living near the forests' edges and the creation of additional protected areas, in order for these two species to have any chance of long-term survival.