Sirdal is a municipality in Vest-Agder county, Norway. Sirdal was separated from Bakke in 1849. Sirdal was divided into Tonstad and Øvre Sirdal on 1 January 1905, but these were again merged to recreate Sirdal on 1 January 1960.It is the northernmost valley in Vest-Agder. At the north end of its long narrow lake, Siredalsvatn, lies the administrative center of the municipality in the village of Tonstad. Bjørnestad is another village lying in Sirdal.
The Old Norse form of the name was Sírudalr. The first element is the genitive case of the river name Síra and the last element is dalr which means "valley" or "dale". The meaning of the rivername is unknown (maybe "strong stream").The coat-of-arms is from modern times. They were granted on 17 January 1986. The arms show three grouse (Lagopus lagopus) as a symbol for the hills and moors, which make up the largest part of the municipality. The grouse is a typical bird for the area.