Rahnsdorf is a German locality (Ortsteil) within the Berlin borough (Bezirk) of Treptow-Köpenick. Until 2001 it was part of the former borough of Köpenick.
The locality was first mentioned in 1375, originally created as fishermen's village, which has its own church. After 1872, when it burned down almost completely, it was rebuilt. In 1902 the Villenkolonie of Wilhelmshagen was built in the east of the village with Tabor Church. In 1920 Rahnsdorf merged into the city of Berlin with the "Greater Berlin Act" and from 1949 to 1990 it was part of East Berlin.
Located in the south-eastern suburb of Berlin, Rahnsdorf is the easternmost locality of the city. The easternmost point is represented by Springeberg, a ground located in front of Falkensee lake, bordering with Woltersdorf and Erkner, two municipalities of Oder-Spree district, Brandenburg. Similar to an exclave it is linked to Berliner mainland with a road (Woltersdorfer Landstraße) forming a strip, as in Steinstücken. The other municipality bordering with Rahnsdorf is Schöneiche, also part of Oder-Spree. Another peculiarity of Rahnsdorfer borders with Brandenburg is represented by Landjägerallee, a road parallel to railway that forms a thin and long strip belonging to Erkner surrounded by Berliner territory. The localities of Treptow-Köpenick bordering with Rahnsdorf are Friedrichshagen, Köpenick and Müggelheim.