Sømna is a municipality in Nordland county, Norway. It is part of the Helgeland traditional region. The administrative center of Sømna is the village of Vik i Helgeland. Other villages in the municipality include Dalbotn, Sund, Vennesund, and Berg.
The municipality of Vik was established on 1 January 1901 when it was separated from the large municipality of Brønnøy. The initial population of Vik was 2,731. In 1941 the municipality was renamed Sømna. On 1 January 1964, Sømna was merged together with Brønnøysund, Velfjord, Brønnøy, and part of northern Bindal. Prior to the merger Sømna had 2,347 residents.