Hamarøy is a municipality in Nordland county, Norway. It is part of the Salten traditional region. The administrative centre of the municipality is the village of Oppeid. Hamarøy was established as a municipality on 1 January 1838 (see formannskapsdistrikt).
The municipality is named after the former island (now peninsula) Hamarøya (Old Norse: Hamarøy), since the first church was built there. The first element is the genitive case of Hǫm, the former uncompounded name of the island. The last element is øy which means "island". The former name of the island is probably identical with the word hǫm which means "thigh/leg (of an animal)" because the island (or a part of it) was shaped in the form of an animal's leg.