Frohnau is a locality in the Reinickendorf borough of Berlin, Germany. It lies in the extreme northern part of the city.

Founded in 1910, Frohnau was created whole as a planned community, corresponding to the early twentieth century idea of a Garden City. Frohnau was founded in the Stolper Heath, which had been bought for the Berlin Terrain Commission by Count Guido Henckel von Donnersmarck in 1907. The competition for the design was won by a plan developed by Joseph Brix and Felix Genzmer. Their concept represented an asymmetrical, seemingly natural development out of the dunes near the Havel River. Even the name "Frohnau" was determined by a contest. In 1920, Frohnau was annexed into the Greater Berlin city-state.

The natural centre of the city has always been the train station and the nearby buildings. The casino tower serves as the symbol of Frohnau. The entire area is noted for its large mansion-like buildings.

The architects responsible for the typical mansions include Walter and Johannes Krüger (the Church of St. John), Hart and Lesser (train station and casino tower), Max Meyer (Buddhist house), Paul Poser, Max Scheidling, and Heinrich Straumer (better known for his work on Berlin's radio tower, Funkturm).