Flå is a municipality in Buskerud county, Norway. The administrative centre of the municipality is the village of Flå. The municipality of Flå was established when it was separated from the municipality of Nes on 1 January 1905. The municipality lies at the most southeasterly point in the valley and traditional region of Hallingdal.
The Old Norse form of the name was Flóða sokn (sokn means parish). This is the plural genitive case of flœð meaning "flood" (probably because flooding has been a problem for many farms in the river valley). Prior to 1921, the name was written "Flaa".The coat-of-arms is from modern times. They were granted on 1 March 1985. The arms show a black bear on a gray/silver background. This was chosen because there used to be many bears in the Vassfaret area. Prior to 1985, the municipality used a logo with a bear walking through the area.
Ancient routes went to Vestlandet through Valdres and Hallingdal and down Røldal to Odda. Reflecting this route, Hallingdal and its neighboring valley of Valdres in Oppland to the north were originally populated by migrants from Vestlandet and spoke a western dialect. In recognition of this, Cardinal Nicholas Breakespear, who was in Scandinavia as papal legate in 1153, included Hallingdal in the diocese of Stavanger.