The hoolock gibbons are three primate species of genus Hoolock in the gibbon family, Hylobatidae, native to eastern Bangladesh, Northeast India, Myanmar, and Southwest China.
In northeast India, the hoolock is found south of Brahmaputra and the North Bank areas and east of the Dibang Rivers. Its range extends into seven states covering Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, and Tripura (The seven northeastern states of India). In Bangladesh, the western hoolock gibbons were distributed across 35 forest fragments. The largest of these (Lawachara and Kaptai) supported 42 and 84 individuals respectively, but 17 of the fragments had less than ten individuals. For a better overview the forest fragments are grouped into 13 areas. All areas are located within Chittagong and Sylhet divisions, mostly near the eastern border of the country. In China, in historical times, the skywalker gibbon was recorded in nine counties in the west bank of the Salween River in westernmost Yunnan province. Based on more recent interview surveys conducted in Oct-Nov 2008 and field surveys conducted in Mar, Apr, and Aug 2009, the current Chinese population of hoolock gibbons was found to be restricted to three counties (Baoshan, Tengchong, and Yingjiang). The population size was estimated to be less than 200 individuals. In Myanmar, all three species of hoolock gibbon can be found in the forested areas west of Thanlwin river. Of all four distribution countries, Myanmar holds the key population of all three species.