Sigdal is a municipality in Buskerud county, Norway. The administrative centre of the municipality is the village of Prestfoss.
The municipality of Sigdal was established on 1 January 1838 (see formannskapsdistrikt). The area of Krødsherad was separated from Sigdal on 1 January 1901. The municipality has common borders with the municipalities of Flå, Krødsherad, Modum, Øvre Eiker, Flesberg, Rollag, and Nore og Uvdal.
The Old Norse form of the name was Sigmardalr or Sigmudalr. The first element is the genitive case of a river name Sigm(a) (now called the Simoa) and the last element is dalr which means "valley" or "dale". The Simoa river runs through Sigdal, flowing in a south-easterly course until it flows into Drammenselva at Åmot in Modum. The meaning of the river name is unknown, but is maybe derived from síga which means to "ooze" or "slide".
The coat-of-arms is from modern times. They were granted on 18 November 1983. The arms show a heraldic image of the mountain that dominates the view around the village, the Andersnatten. The profile of the mountain is yellow with a blue-colored sky above.