The Nilgiris Biosphere Reserve was constituted by UNESCO in September 1986. It is the first biosphere reserve in India and it is in the Western Ghats, Nilgiri Hills range of South India. The Western Ghats, Nilgiri Sub-Cluster (6,000+ km²), conjoining the Nilgiri Biosphere Reserve, is under consideration by the UNESCO World Heritage Committee for selection as a World Heritage Site.

The reserve encompasses 5,520 km² in the states of Tamil Nadu (2537.6 km²), Karnataka (1527.4 km²) and Kerala (1455.4 km²). It forms an almost complete ring around the Nilgiri Plateau. The biosphere lies Between 10°50′N and 12°16′N latitude and 76°00′E to 77°15′E longitude. Central location:11°33′00″N 76°37′30″E. The Tamilnadu Part covers parts of The Nilgiris (Mudumalai WL Sanctuary and National Park (321.1), Mukurthi National Park (78), Nilgiris North (448.3), Nilgiris South(198.8)), Erode (Sathyamangalam (745.9), Erode(49.3)) and Coimbatore (696.2) Districts in Tamil Nadu.

The reserve extends from the tropical and subtropical moist broadleaf forests, tropical moist forests of the western slopes of the Ghats to the tropical and subtropical dry broadleaf forests tropical dry forests on the east slopes. Rainfall ranges from 500mm to 7000mm per year. The reserve encompasses three ecoregions, the South Western Ghats moist deciduous forests, South Western Ghats montane rain forests, and South Deccan Plateau dry deciduous forests. The habitat types include montane rain forest, semi-evergreen moist forest, thorn forest and scrub, montane grassland, and high-elevation, Shola forests.

Fauna includes over 100 species of mammals, 350 species of birds, 80 species of reptiles, about 39 species of fish, 31 amphibians, 316 species of butterflies. It includes the tiger, Asian elephant, and Nilgiri tahr.

The Nilgiri Biosphere Reserve is very rich in plant diversity. About 3,300 species of flowering plants can be seen here. Of the 3,300 species 132 are endemic to the reserve. The genus Baeolepis is exclusively endemic to the Nilgiris. Some of the plants entirely restricted to the Nilgiri Biosphere Reserve include species of Adenoon, Calacanthus, Baeolepis, Frerea, Jarodina, Wagatea, Poeciloneuron, etc. Of the 175 species of orchids found in the Nilgiri Biosphere Reserve, eight are endemic. These include endemic and endangered species of Vanda, Liparis, Bulbophyllum, Spiranthes and Thrixspermum. The sholas of the reserve are a treasure house of rare plant species.

The inclusion of areas adjoining the legally designated reserve forests, national parks and sanctuaries as buffer zone and restoration zone poses a whole range of management problems that need to be tackled for effective conservation and protection of forests and wildlife in NBR. Some of the issues that leave far-reaching and undesirable impacts on the Biosphere biodiversity are:

• Human pressures, particularly from forest dwellers in the core zone.
• Biotic interference by way of grazing, fire, illicit felling, leading to habitat degradation.
• Fragmentation of habitats resulting from unsustainable developments happening in buffer zone.
• Encroachment of buffer zone that is crucial migratory tract of animals like elephants leading to habitat of man-animal conflict.

In 1986, a group of 21 islets lying off the Tamil Nadu coast between Thoothukudi and Dhanushkodi were declared the Gulf of Mannar Marine National Park. The park and its 10 km buffer zone were declared a Biosphere Reserve in 1989. The 21 islands are 1 to 10 KM away from the coast of mainland and their extent varies from 0.25 ha to 130 ha. The Gulf of Mannar Marine National Park lies within 08o47’ to 09o15’ N; and 78o12’ to 79o14’ E .

The Gulf of Mannar is a large shallow bay forming part of the Laccadive Sea in the Indian Ocean. It lies between the south-eastern tip of India and the west coast of Sri Lanka. A chain of low islands and reefs known as Adam's Bridge, also called Ramsethu, which includes Mannar Island, separates the Gulf of Mannar from Palk Bay, which lies to the north between India and Sri Lanka. The estuaries of Thamirabarani River of south India and the Aruvi Aru River of Sri Lanka drain into the Gulf.

The Gulf of Mannar Marine National Park has the core area of about 560 sq.KM from Rameswaram to Tutucorin lying within the Gulf of Mannar Biosphere Reserve covering an area of 10,500 Sq.KM. on the south-east coast of India. It covers the coast of Rameswaram, Tutucorin, Tirunelveli and Kanyakumari. It is one of the world’s richest regions from marine bio diversity perspective and the first marine Biosphere Reserve in Southeast Asia. The Biosphere Reserve comprises 21 islands with estuaries, mudflats, beaches, forests of the near shore environment, including marine components like algal communities, sea grasses, coral reefs, salt marshes and mangroves.

The Gulf of Mannar is known to harbour over 3,600 species of flora and fauna, making it one of the richest coastal regions in Asia. 117 hard coral species have been recorded in the Gulf of Mannar. Sea turtles are frequent visitors to the gulf as are sharks, dugongs, anddolphins. However, the combined effects of 47 villages, with a total population of around 50,000 has meant that overharvesting of marine species has become a problem. Fish catches have declined, as have pearl oyster, gorgonian coral, and acorn worm populations. Local fishermen rely on the reef to feed their families, but destructive fishing methods combined with the stress of pollution and coral mining have meant both nearshore and offshore catches have decreased.Endangered species include dolphins, dugongs, whales and sea cucumbers.

The Gulf of Mannar is known for its pearl banks of Pinctada radiata and Pinctada fucata for at least two thousand years. Pliny the Elder (23–79) praised the pearl fishery of the gulf as most productive in the world.[5][6][7] Although extraction of natural pearls is considered too expensive in most parts of the world, it is still conducted in the gulf.

The chief seaports on the Gulf of Mannar are Thoothukudi (Tuticorin) in Tamil Nadu, and Colombo in Sri Lanka. While these ports can accommodate deep-draft vessels, the shallow Palk Strait can only accommodate small shallow-draft vessels. In July 2005, the Indian Government took preliminary steps to go ahead with the Sethusamudram Shipping Canal Project, which would create a deep channel linking the Gulf of Mannar to the Bay of Bengal. Project boosters emphasize the benefits of a direct shipping route that connects India's east and west coasts without the long trip around Sri Lanka; environmentalists have warned against the grave damage such a project could cause to the sea life and fisheries of the Palk Strait and the Gulf.

The total area of the Bio-sphere reserve is 3500.36 Sq. K.m out of which 1828 Sq. Kms. is in Kerala and 1672.36 Sq. Kms. is in Tamil Nadu vide Government of India Notification F.No.9/15/99-CS/BR dated 04.08.2005. The Bio-sphere Reserve now covers parts of Tirunelveli and Kanyakumari District in Tamil Nadu and Thiruvananthapuram, Kollam and Pathanamthitta District in Kerala. The Biosphere lies Between 8° 8' to 9° 10' North Latitude and 76° 52' to 77° 34' East Longitude. Central location is 8°39′N 77°13′E .

The Western Ghats, Agasthyamalai Sub-Cluster, including all of Agasthyamalai Biosphere Reserve, is under consideration by the UNESCO World Heritage Committee for selection as a World Heritage Site. Agasthyamala is located in this biosphere area.

The Biosphere reserve is split into three major zones viz. Core Zone, Buffer Zone and Transition Zone.