Hemsedal is a municipality in Buskerud county, Norway. It is part of the traditional region of Hallingdal. The administrative centre of the municipality is the village of Trøym. In 1897, Hemsedal was separated from the municipality of Gol to become a municipality of its own.
Hemsedal is the second largest ski resort in Norway. From the museum farm Øvre Løkji, there are several trails up into the mountains.
The Old Norse form of the name was Hemsudalr. The second element is dalr, which means "valley" or "dale"; the first element is usually taken as the genitive case of the river name Hemsa (now Hemsil) of unknown derivation, although Sophus Bugge believed that it might derive from the Old Norse hemsa, hefnsa or hofn, meaning "going to pasture".
The Norwegian word hems ("bed built in a small loft room") is named after the valley of Hemsedal.
The coat-of-arms is from modern times. The arms were granted on 2 October 1992 and were designed by Stein Davidsen. The arms show a gold lynx head on a red background.