The Nicobar Islands are an archipelagic island chain in the eastern Indian Ocean and one of the most isolated in the world. They are located in Southeast Asia, 150 km north of Aceh on Sumatra, and separated from Thailand to the east by the Andaman Sea. Located 1,300 km southeast of the Indian subcontinent, across the Bay of Bengal, they form part of the Union Territory of Andaman and Nicobar Islands, India.

The Nicobar Islands are part of a great island arc created by the collision of the Indo-Australian Plate with Eurasia. The collision lifted the Himalayas and most of the Indonesian islands, and created a long arc of highlands and islands, which includes the Arakan Yoma range of Burma, the Andaman and Nicobar islands, and the islands off the west coast of Sumatra, including the Banyak Islands and Mentawai Islands.

On 26 December 2004, the coast of the Nicobar Islands was devastated by a 10–15 m high tsunami following the 2004 Indian Ocean earthquake. At least 6,000 people were killed on the Andaman and Nicobar Islands with reports putting the death toll on Katchal Island alone at 4,600.

Several islands were heavily damaged with initial reports of islands broken in two or three pieces and coral reefs moved above water. Teressa Island was said to have been split into two pieces and Trinkat Island into three pieces. Some estimates said that the islands were moved as much as 100 feet (30 m) by the earthquake and tilted.

Indira Point subsided 4.25 m and the lighthouse there was damaged.

On 31 May 2013 it was reported that Nicobar Islands have been declared as World Biosphere Reserve by UNESCO.

Together with the Andaman Islands, they became a union territory of India in 1950.