Nissedal is a municipality in Telemark county, Norway. It is part of the traditional region of Vest-Telemark. The administrative centre of the municipality is the village of Treungen. The municipality of Nissedal was established on January 1, 1838 (see formannskapsdistrikt).

The modern form of the name stems from Old Norse Nizidalr. The first element is the name of the lake Nizir, possibly from *Nið-sær, which is now called Nisser, and the last element is dalr "valley, dale".

Nissedal is a municipality covering an area of 905,2 km² in Telemark County. Nissedal municipality borders Kviteseid to the north, Fyresdal to the west, Drangedal and Gjerstad to the east, and borders Vegårshei and Åmli to the south. Nisser lake, which is 40 kilometres in length and 250 meters deep, is the largest in the county and the seventh largest lake in Norway.

The coat of arms was granted on October 30, 1992, and was designed by Halvor Holtskog jr. The arms shows three red nisseluer, traditional red woolen hats often associated with the nisse, which were commonly worn until the late 19th century by farmers and common folk. It is a canting arms, as the name Nissedal has been "translated" into a visual pun with the three woolen hats, in spite of the name having nothing to do with the folkloric nisse.

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