Beiarn is a municipality in Nordland county, a part of the traditional district of Salten, Norway. Beiarn is also a part of the Bodø Region, a statistical metropolitan region. The administrative centre of the municipality is the village of Moldjord. Other villages in Beiarn are Høyforsmoen, Trones, and Tverrvika.

Beiarn is located just north of the Arctic Circle, along the Beiar River including the Beiar Valley and some surrounding areas in the Saltfjellet mountains. The river is one of the best salmon rivers in Northern Norway. There are several large lakes in Beiarn including Arstaddalsdammen, Litle Sokumvatnet, and Ramsgjelvatnet.

The Saltfjellet–Svartisen National Park is partially located in Beiarn. The world´s most northern naturally occurring elm forest grows in the Arstadlia nature reserve, where the rich vegetation also includes orchids.

The area offers many outdoor activities to visitors, including fishing, caving, and mountain walking. The Beiarn farm museum includes an overview of Beiarn´s cultural history, from the Viking Age through to the middle of the 20th century.