Skien is a city, municipality and county capital in Vestfold and Telemark county. Skien was the administration center in the province that went under the names Skiensysla, Bratsberg county, Bratsberg county and Telemark county from the Middle Ages until 2020.

The ski borders in the north to Midt-Telemark and Kongsberg, in the east to Siljan, in the south to Porsgrunn and Bamble, and in the west to Drangedal and Nome. Historically, today's Skien was partly considered to be Grenland and partly to Grenmar or Skiensfjorden, but over time the whole area was seen as part of Grenland. Grenland was from the 16th century in ecclesiastical and administrative units called Nedre Telemark, and thus this also established itself as a name for the area.

The city is one of Norway's oldest, and the settlement grew around the year 1000. It is one of the few medieval cities in Norway that was not founded by a king. Through the lumber and sawmill industry, Skien became one of Norway's most important commercial and cultural centers from the 16th century, and retained its position as one of Norway's foremost cities until the beginning of the 19th century. Today, ICT and other knowledge-based activities are about to take over as the most important business route in Skien.

Skien is known as the birthplace of the playwright Henrik Ibsen, who often draws motifs from Skien in his poetry, and the municipality spends a lot of resources on managing and communicating the artist's life and works. The polar explorer Hjalmar Johansen was also from Skien, and he co-founded the Sports Association Odd. Norway's oldest existing football club, Odds ballklubb, has its origins in this sports association. Skien has three large theater buildings, the Ibsen House from the 1970s, the Festival which was completed in 1891 and the Ibsen Theater on Kloster√łya which was completed in 2016.

The municipality and the city are Norway's 11th largest, with 55,745 inhabitants as of 1 January 2016. The city of Skien is part of a contiguous urban area in the municipalities of Skien, Porsgrunn and Bamble, and the town of Porsgrunn / Skien is the seventh largest in the country with 93,255 inhabitants per. 1 January 2019 (of which in Skien 49 265, in Porsgrunn 33 813 and in Bamble 10 177).