Grey Langur (Dufresne) also commonly known as Hanuman langur stretches from the Himalayas in the north to Sri Lanka in the south and from Bangladesh in the east to Pakistan in the west. They can be seen on trees and forests of NEERI solitary as well as in groups. Grey Langurs are large and fairly terrestrial; inhabiting forest, open lightly wooded habitats, and urban areas on the Indian subcontinent. Gray Langurs are primarily herbivores. Feeds on leaves of Trees, leaf buds of herbs, but also eats coniferous needles and cones, fruits and fruit buds, evergreen petioles, shoots and roots, seeds, grass, bamboo, fern rhizomes, mosses, and lichens.

Hanuman Langurs are largely gray with a black face and ears. North Indian gray Langurs have their tail tips looping towards their head during a casual walk. The head-and-body length is from 51 to 79 cm (20 to 31' '). Their tails are 69 to 102 cm (27 to 40' ') is always longer than their bodies. At 26.5 kg (58 lb).The average weight of gray langurs is 18 kg (40 lb) in the males and 11 kg (24 lb) in the females.

In some areas, reproduction is year-around. Year-round reproduction appears to occur in populations that capitalize on human-made foods. Other populations have seasonal reproduction. In one-male groups, the resident male is usually the sole breeder of the females and sires all the young. In multiple-male groups, the highest-ranking male fathers most of the offspring, followed by the next-ranking males and even outside males will father young. Higher-ranking females are more reproductively successful than lower-ranking ones.

Females signal that they are ready to mate by shuddering the head, lowering the tail, and presenting their anogenital regions. Such solicitations do not always lead to copulation. When langurs mate, they are sometimes disrupted by other group members. The gestation period of gray langur lasts around 200 days.

The heaviest langur ever recorded was a male Nepal gray langur. In India, gray langurs number are around 300,000.India has laws prohibiting the capturing or killing of langurs, but they are still hunted in some parts of the country.