Hadsel (Northern Sami: Ulbi) is a municipality in Nordland county, Norway. It is part of the traditional district of Vesterålen. The administrative centre of the municipality is the town of Stokmarknes. Some of the main villages in Hadsel include Fiskebøl, Jarstad, Grønning, Grytting, Hanøyvika, Hennes, Kaldjorda, Melbu, Sanden, and Sandnes.

The municipality is the southernmost municipality in the Vesterålen region. It is spread over several main islands: Hadseløya, Børøya, Hinnøya, Langøya, and Austvågøya. About 70% of the population live on Hadseløya island. Hadseløya island is connected to Langøya by the Hadsel Bridge and Børøy Bridge. Also, the Stokmarknes Airport, Skagen, is located nearby. It is the busiest small aircraft airport in Norway, serving 100,000 passengers annually (1997).

The 567-square-kilometre (219 sq mi) municipality is the 191st largest by area out of the 357 municipalities in Norway. Hadsel Municipality is the 130th most populous municipality in Norway with a population of 8,236. The municipality's population density is 14.5 inhabitants per square kilometre (38/sq mi) and its population has increased by 1.5% over the previous 10-year period.

Hadsel was established as a municipality on 1 January 1838 (see formannskapsdistrikt law). The northern district of Hadsel was separated in 1841 to form the new Sortland Municipality. During the 1960s, there were many municipal mergers across Norway due to the work of the Schei Committee. On 1 January 1963, the Indre Eidsfjord district of Hadsel (population: 1,360) was transferred to Sortland Municipality.

The municipality (originally the parish) is named after the old Hadsel farm (Old Norse: Hǫfðasegl) since the first Hadsel Church was built there. The first element is the genitive case of hǫfði which means "high and steep cliff" or "head". The last element is segl which means "sail". (A cliff near the farm has been compared in form to a sail.)

The coat of arms was granted on 11 March 1976. The official blazon is "Azure, four annulets Or, two and two" (Norwegian: I blått fire gull ringer - 2,2). This means the arms have a blue field (background) and the charge is four rings (two over two). The charge has a tincture of Or which means it is commonly colored yellow, but if it is made out of metal, then gold is used. The blue color in the field symbolizes the importance of sea for this island municipality. The four rings represent the four main islands of that make up Hadsel: Hadseløya, Austvågøya, Hinnøya, and Langøya. The arms were designed by Øystein Bottolfsen.

The Church of Norway has three parishes (sokn) within Hadsel Municipality. It is part of the Vesterålen prosti (deanery) in the Diocese of Sør-Hålogaland.

The municipality is located upon four main islands in the Vesterålen archipelago: Hinnøya, Langøya, Hadseløya, and Austvågøya, plus the small islands of Børøya and Brottøya. The 1,135.8-metre (3,726 ft) tall mountain Higravtindan is the highest point in the municipality. It is located on the border with Vågan Municipality and it is one of the tallest mountains in the whole region. Sortland Municipality lies to the north, Bø Municipality lies to the west, Vågan Municipality lies to the south, and Lødingen Municipality lies to the east.