Agder is a county and traditional region in the southern part of Norway and is coextensive with the Southern Norway region. The county was established on 1 January 2020, when the old Vest-Agder and Aust-Agder counties were merged. Since the early 1900s, the term Sørlandet has been commonly used for this region, sometimes with the inclusion of neighbouring Rogaland. Before that time, the area was considered a part of Western Norway.