Tønsberg is a city, municipality and headquarters for the office of state administrator in Vestfold and Telemark county. With a population of 53,018 (as of 1 January 2020), it is Norway's tenth largest urban area, while the municipality, with a population of 56,293 (as of 1 January 2020), is Norway's seventeenth largest. The municipality borders in the west on the municipalities of Sandefjord and Larvik, in the north on Horten and Holmestrand, and in the south on Færder. East of Tønsberg is the Oslo Fjord and the middle fjord borders the municipality there towards Moss, Råde and Fredrikstad.

Tønsberg was for a long time a town with a very limited area, and the urban development already in the 19th century went beyond the city limits, into the municipalities Færder (formerly Nøtterøy) and Sem. An urban expansion in 1877 gave Tønsberg a strip of Nøtterøy with important maritime industrial areas. In 1988, the municipalities of Tønsberg and Sem were merged. On 1 January 2020, Tønsberg and Re municipalities merged into the new Tønsberg municipality and after the merger are the only municipality in Vestfold that borders all the other Vestfold municipalities.

Tønsberg is a medieval town and is considered Norway's oldest town; according to Snorre, the town was founded before the year 871. The Oseberg ship, Norway's most spectacular archaeological find, was excavated in Slagendalen, and the site, Oseberghaugen, is adapted for visitors.

Tønsberg was Vestfold's county capital until the county was closed down on 1 January 2020. Today, Tønsberg houses one of two county houses in the new Vestfold and Telemark county municipalities.

Tønsberg has large agricultural areas, and important wetlands for bird life.