Nilgiri Biosphere Reserve is a biosphere reserve in the Nilgiri Mountains of the Western Ghats in South India. It is the largest protected forest area in India, spreading across Tamil Nadu, Karnataka and Kerala. It includes the protected areas Mudumalai National Park, Mukurthi National Park, Sathyamangalam Wildlife Sanctuary in Tamil Nadu; Nagarhole National Park, Bandipur National Park, both in Karnataka; Silent Valley National Park, Aralam Wildlife Sanctuary, Wayanad Wildlife Sanctuary, and Karimpuzha Wildlife Sanctuary in Kerala.
An ecosystem of the hill ranges of Nilgiris and its surrounding environments covering a tract of over 5,000 km (1,900 sq mi) was constituted as Nilgiris Biosphere Reserve by UNESCO in September 1986 under Man and Biosphere Programme. Nilgiris Biosphere Reserve is India's first and foremost biosphere reserves with a heritage, rich in flora and fauna. Tribal groups such as the Toda, Kotas, Irulla, Kurumba, Paniya, Adiyan, Edanadan Chettis, Allar, and Malayan are native to the reserve.