Southern Norway is the geographical region (landsdel) along the Skagerrak coast of southern Norway. The region is an informal description since it does not have any governmental function. It roughly corresponds to the old petty kingdom of Agder being coextensive with the county, as well as the two former counties of Vest-Agder and Aust-Agder. From New Year 2020, the two counties have been merged into one county, Agder. The total combined area of Vest-Agder and Aust-Agder counties is 16,493 square kilometres (6,368 sq mi). The name is relatively new, having first been used in Norway around 1900.

Vest-Agder was one of 18 counties (fylker) in Norway up until 1 January 2020, when it was merged with Aust-Agder to form Agder county. In 2016, there were 182,701 inhabitants, around 3.5% of the total population of Norway. Its area was about 7,277 square kilometres (2,810 sq mi). The county administration was located in its largest city, Kristiansand.