Nīas (Indonesian: Pulau Nias, Nias language: Tanö Niha) is an island off the western coast of Sumatra, Indonesia. Nias (Kepulauan Nias) is also the name of the archipelago, containing the Hinako archipelago.

Nias Island covers an area of 5,121.3 km² (1,977.3 sq mi) (including minor offshore islands) which is mostly a lowland area on average 800 m (2,600 ft) above sea level. There were 756,762 inhabitants on the island (including minor offshore islands) at the 2010 Census.

It is located in a chain of islands parallel to the west coast of Sumatra; Simeulue is about 140 km (87 mi) northwest, and the Batu Islands are located about 80 km (50 mi) southeast. This chain, which resurfaces in Nusa Tenggara in the mountainous islands of Sumba and Timor, is the forearc of the South Sumatra Basin along the Sunda Trench subduction zone.

At Nias the oceanic plate is being obliquely subducted under the Asian Plate at the rapid rate of 52 mm (2.0 in) a year (Milsom).

Nias is the largest of the islands off Sumatra that are part of North Sumatra province. This area consists of 131 islands and Nias Island is the biggest. The population in this area is about 639,675 people (including Ono Niha – the native inhabitant of the Island, Malay, Batak, and Chinese).