Brønnøysund (Southern Sami: Brïenne) is a town and administration center in Brønnøy municipality in Nordland. The city is located on the coast and is profiled as «The coastal city in the middle of Norway». Brønnøysund is also the regional center for Sør-Helgeland. The town of Brønnøysund has 5,071 inhabitants as of 1 January 2020.

Brønnøysund was granted charging station status in 1923 and was its own municipality from 1 January 1923 to 31 December 1963. From 1 January 1964, the city became an administrative center in the new Brønnøy municipality, and at the same time lost its city status. From the year 2000, Brønnøysund has again city status following a decision by the municipal council. The city can celebrate its 100th anniversary in 2023. From Brønnøysund you can see the city's famous landmark Torghatten. The city is also known for housing most of the state register agency Brønnøysundregistrene.

Brønnøysund is named after the island Brønnøy, pronounced [brønn'øye] and [bryŋŋ'øya]. The name form Brunney is written down in 1334, from Old Norse brunnr which means "origin", "source". The name means that seafarers could find drinking water on these islands. It was thus originally the name of the island, where the farm and church site Brønnøy was later laid. The name forms Brønnø and Brønnøy have been used continuously from the entry into force of the Presidency Act in 1838 until today. In a list from 1808, the postal service used the name Brønøe. It was changed to Brønnø in the postage list from 1889, and Brønnøy on 15 December 1908.