Alstahaug is a municipality in Nordland county, Norway. It is part of the Helgeland region. The administrative centre of the municipality is the town of Sandnessjøen. Other villages in Alstahaug include Søvika and Tjøtta.
The administrative centre of Alstahaug is the town Sandnessjøen which is situated on the island of Alsta. The characteristic Seven Sisters mountain range is found on the eastern part of the island. Local legend has made this chain of peaks into seven sisters, two adjacent peaks representing twin sisters.
The island is connected to the mainland via the impressive Helgeland Bridge along Norwegian County Road 17. The Sandnessjøen Airport, Stokka is located just south of Sandnessjøen.