Schleswig-Flensburg (German pronunciation: [ˈʃleːsvɪç ˈflɛnsbʊʁk] ⓘ; Danish: Slesvig-Flensborg) is a district in Schleswig-Holstein, Germany.

It is bounded by (from the south and clockwise) the districts of Rendsburg-Eckernförde, Dithmarschen and Nordfriesland, the Region Syddanmark in Denmark, the city of Flensburg and the Baltic Sea.

Written history in the area began about 800 AD, when the Danish Viking settlement of Haithabu was founded.

Due to the proximity of Denmark and the regional history there is a large percentage of Danish inhabitants.

Angeln was the ancient home of the Germanic people known as the Angles, who migrated to England in the early Middle Ages.