A langur is a type of leaf-eating monkey that belongs to the subfamily Colobinae, which includes five genera and at least forty-six species and forty-one subspecies. Langurs are "Old World" monkeys with an extremely large family of primates with 159 species and 23 genera presently recognized in Asia. They have a multi-chambered stomach that allows them to digest the stodgy plant food in between feeding times, which is the reason for their big belly. Langurs have a high fiber diet, which can range from leaves and unripe fruits to bark and blossom, and are slowly digested by the Langurs unique gut flora during their long rest periods. Some key features of langurs include:

• Appearance: Langurs have a slender body with a long tail, and their size varies depending on the sex, with males always larger than females. The head-and-body length is from 51 to 79 cm (20 to 31 in), and their tails, at 69 to 102 cm (27 to 40 in), are always longer than their bodies.

• Social structure: Langurs exist in three types of groups: one-male groups, multiple-male groups, and all-male groups.

• Habitat: Langurs can be found near roads and can become victims of automobile accidents. They are considered sacred in the Hindu religion and are sometimes kept for religious purposes by Hindu priests and for roadside performances.

There are several species of langurs, including the Hanuman langurs, which are native to the Indian subcontinent and constitute the genus Semnopithecus. Leaf monkeys of genus Trachypithecus are also called brow-ridged langurs and live in Southeast Asia from Bhutan and southern China to Java. Other langurs belong to the genera Pygathrix, Rhinopithecus, Nasalis, and Simias and include the proboscis monkey and simakobu.