Doucs live in the forest canopy - the highest layer of leaves and branches - in Laos, Vietnam and Cambodia. They spend almost their whole lives up in the trees, leaping between branches with great agility. Each leap can cover several metres.
They are leaf-eaters. Their digestive systems are specially designed to break down tough leaves that would upset most other animals' stomachs. They also eat flowers, seeds and unripe fruit. Unlike many monkeys, they don't eat insects at all.
Douc langurs live in small groups of usually 4 to 15 animals. They are social and communicative, using facial expressions and postures to talk to each other. They groom each other carefully, picking through fur - this is their way of showing friendship and trust.
Douc langurs are very sensitive to changes in their forest. They need large, undisturbed areas of jungle to find enough leaves and space. Conservation groups in Laos work to protect the forests where doucs live, partly because they are a signal of how healthy the whole forest is.