Søgne is a former municipality in the old Vest-Agder county, Norway. The municipality existed from 1838 until 2020 when it was merged with the municipalities of Songdalen and Kristiansand into the "new" Kristiansand municipality in what is now Agder county. It was located in the traditional district of Sørlandet, just outside of the city of Kristiansand. The administrative centre of the municipality was the village of Tangvall. Other villages in Søgne include Ausviga, Eig, Høllen, Langenes, Lohne, Lunde, Ny-Hellesund, Trysnes, Vedderheia, Ålo, and Åros.
Prior to its dissolution in 2020, the municipality was the 354th largest by area out of the 422 municipalities in Norway. Søgne is the 103rd most populous municipality in Norway with a population of 11,321. The municipality's population density is and its population has increased by 16.2% over the last decade.
The parish of Sygne (later spelled Søgne) was established as a municipality on 1 January 1838 (see formannskapsdistrikt law). on 1 July 1913, the northern half of Søgne (population: 822) was separated to form the new municipality of Greipstad. This left Søgne with 2,609 residents. During the 1960s, there were many municipal mergers across Norway due to the work of the Schei Committee. Søgne municipality remained generally the same during this time, however, there were a couple of small changes to the municipal boundaries. On 1 January 1964, the Stubstad area of neighboring Holum municipality (population: 9) and the Brunvatne area of neighboring Øyslebø municipality (population: 44) were both transferred to Søgne municipality. Then on 1 January 1965, the unpopulated Svalemyren area of neighboring Mandal municipality was transferred to Søgne.
On 1 January 2020, the three neighboring municipalities of Kristiansand, Songdalen, and Søgne merged to form one large municipality called Kristiansand.
The municipality (originally the parish) is named after the old Søgne farm (Sygna) since the Old Søgne Church was built there. The name comes from the local river Sygna (now called Søgneelva).