The Hanuman langur is an acrobatic and adaptable leaf-eating monkey and it is widely distributed in diverse ecological settings across South Asia. These amazing monkeys can be seen from the cool snow-clad peaks of the majestic Himalayas in Nepal to the fringes of the scorching Thar Desert near Jodhpur in India. They are primarily vegetarians and they are adapted to digest all forms of leafy diet resembling the ruminants. They prefer to live in dry deciduous tropical forests and they are also uniquely adapted to live with humans in congested cities of India. These monkeys are revered by Hindus as the living incarnation of Hanuman, the monkey God. The author, an international primatologist with three decades of field research experience from Asia, Africa and South America, has studied the langurs in India. In this monograph, the author has synthesized his long-term field research on the Hanuman langurs of India and presented data on population dynamics, ecology, social behavior and conservation. Hence this monograph should serve as an introductory and reference text on primatology and animal behavior related courses in colleges, universities and institutes of higher learning globally