The Hoolock Gibbon (Hylobates hoolock), also known as just the Hoolock, is a primate species from the family of the gibbons (Hylobatidae). It is sometimes classified as the only species in the genus Bunopithecus, but more recent classifications make this a subgenus of Hylobates.

Hoolocks are he second largest gibbon, after the Siamang. They reach a size of 60 to 90 cm and weigh up to 9 kg. The genders are about the same size, but they differ considerably in coloration: males are black colored with remarkable white brows, while females have a grey-brown fur, which is darker at the chest and neck. White rings around the eyes and around the mouth give their face a mask-like appearance.

The range of the Hoolock is the most northwestern of all the gibbons, extending from northeast India, to Myanmar. Small populations (in each case few hundred animals) live also in the eastern Bangladesh and in southwest China. Like the other gibbons, they are diurnal and arboreal, brachiating through the trees with their long arms. They live together in mongamous pairs, which stake out a territory. Their calls serve to locate family members and ward off other gibbons from their territory. Their diet consists mainly of fruits, insects and leaves.

Young Hoolocks are born after a seven month gestation, with a milky white fur. After about six months their fur turns black. After 8 to 9 years they are fully mature and their fur reaches its final coloration. Their life expectancy in the wild is about 25 years.

There are two subspecies of Hoolock:

• Hylobates (Bunopithecus) hoolock hoolock
• Hylobates (Bunopithecus) hoolock leuconedys