Grenland is a traditional district in the county of Telemark, in the south of Norway. Located in the southeastern part of the county, Grenland is composed of the municipalities Skien, Porsgrunn, Bamble, Nome and Siljan. Sometimes the municipalities Kragerø and Drangedal are considered being part of the area. The region encompasses 1,794 km² and has 122,978 inhabitants (2004), which translates as 12% of the area and 64% of the population of Telemark.
Grenland is the core of a slightly larger traditional district known as Nedre Telemark ("Lower Telemark") which also includes Bø, Sauherad and Heddal.
In the early Viking Age, before Harald Fairhair, Grenland, was a petty kingdom. Originally Grenland was probably the name of the region surrounding the lake Norsjø in Nedre Telemark, however, not identical with Grænafylket which also included the coastal villages. Grænafylket (or Grenafylket) contained the coastal region Vestmar and the landscapes further inland.
Vestmar is assumed to signify the land to the west of the sea (mar), however sea in this case should be interpreted as fjord, i.e. Langesundsfjorden. Vestmar was described as a county already in the 8th century AD.
The name Grenland is derived from a people, the Grener, i.e. "the land of the Grener". It is mentioned as a Gothic nation by Jordanes in his work Getica from about 551 AD: "Sunt quamquam et horum positura Granii, Agadii, Eunixi, Thelae, Rugi, Harothi, Ranii." (Getica, III:24)