Tunsberg is a diocese of the Church of Norway. It includes all of the parishes located within the counties of Vestfold and Buskerud, with the cathedral located in the city of Tønsberg. The Diocese of Tunsberg consists of the cathedral deanery and eight rural deaneries.

The Church of Norway is an evangelical Lutheran denomination of Protestant Christianity and by far the largest Christian church in Norway. The church became the state church of Norway around 1020, and was established as a separate church intimately integrated with the state as a result of the Lutheran reformation in Denmark–Norway which broke ties with the Holy See in 1536–1537; the King of Norway was the church's head from 1537 to 2012. Historically the church was one of the main instruments of royal power and official authority, and an important part of the state administration; local government was based on the church's parishes with significant official responsibility held by the parish priest.