Spitsbergen (Urban East Norwegian: [ˈspɪ̀tsˌbærɡn̩]; formerly known as West Spitsbergen; Norwegian: Vest Spitsbergen or Vestspitsbergen [ˈvɛ̂stˌspɪtsbærɡn̩], also sometimes spelled Spitzbergen) is the largest and the only permanently populated island of the Svalbard archipelago in northern Norway in the Arctic Ocean.

Constituting the westernmost bulk of the archipelago, it borders the Arctic Ocean, the Norwegian Sea and the Greenland Sea. Spitsbergen covers an area of 37,673 km² (14,546 sq mi), making it the largest island in Norway and the 36th largest in the world. The administrative centre is Longyearbyen. Other settlements, in addition to research outposts, are the mining community of Barentsburg, the research community of Ny-Ålesund, and the mining outpost of Sveagruva. Spitsbergen was covered in 21,977 km² (8,485 sq mi) of ice in 1999, which was approximately 58.5% of the island's total area.

The island was first used as a whaling base in the 17th and 18th centuries, after which it was abandoned. Coal mining started at the end of the 19th century, and several permanent communities were established. The Svalbard Treaty of 1920 recognized Norwegian sovereignty and established Svalbard as a free economic zone and a demilitarized zone.

The Norwegian Store Norske and the Russian Arktikugol are the only mining companies at Spitsbergen. Research and tourism have become the important supplementary industries, featuring among others the University Centre in Svalbard and the Svalbard Global Seed Vault. No roads connect the settlements; instead snowmobiles, aircraft and boats serve as local transport. Svalbard Airport, Longyearbyen provides the main point of entry and exit.

The island has an Arctic climate, although with significantly higher temperatures than other places at the same latitude. The flora benefits from the long period of midnight sun, which compensates for the polar night. Svalbard is a breeding ground for many seabirds and also supports polar bears, arctic foxes, reindeer, and marine mammals. Six national parks protect the largely untouched, yet fragile environment. The island has many glaciers, mountains, and fjords.

The Dutch navigator Willem Barentsz gave Spitsbergen its name when he discovered it in 1596. The name Spitsbergen, meaning "pointed mountains" (from the Dutch spits – pointed, bergen – mountains), at first applied both to the main island and to the associated archipelago as a whole. In the 17th and 18th centuries, English whalers referred to the islands as "Greenland", a practice still followed in 1780 and criticized by Sigismund Bacstrom at that time. The "Spitzbergen" spelling was used in English during the 19th century, for instance by Beechey, Laing, and the Royal Society.

In 1906 the Arctic explorer Sir Martin Conway regarded the Spitzbergen spelling as incorrect; he preferred Spitsbergen, as he noted that the name was Dutch, not German. This had little effect on British practice. In 1920 the international treaty determining the status of the islands was entitled the "Spitsbergen Treaty". The islands were generally referred to in the United States as "Spitsbergen" from that time, although the spelling "Spitzbergen" also commonly occurred through the 20th century.

The Norwegian administrating authorities named the archipelago Svalbard in 1925, the main island becoming Spitsbergen. By the end of the 20th century, this usage had become common.