The Nicobar Islands are an archipelagic island chain in the eastern Indian Ocean. They are located in Southeast Asia, 150 kilometres north of Aceh on Sumatra, and separated from Thailand to the east by the Andaman Sea.
The Nicobar Islands are recognised as a distinct terrestrial ecoregion, the Nicobar Islands rain forests, with many endemic species.
The vegetation of the Nicobars is typically divided into the coastal mangrove forests and the interior evergreen and deciduous tropical and subtropical moist broadleaf forests. Additionally, several islands contain extensive inland grasslands, though these are thought to have resulted from human intervention.
As a result of lower sea levels during the ice ages, the Andaman Islands were linked to the Southeast Asian mainland, but it is not believed that the Nicobar Islands ever had a land bridge to the continent. Lower sea levels did link the islands to one another: Great Nicobar and Little Nicobar were linked to each other, and Nancowry, Chaura, Katchall, Trinka, Camorta, and the nearby smaller islands were linked to one another as well.