Karl Marx-Hof is one of the best-known Gemeindebauten (municipal tenement complexes) in Vienna, situated in Heiligenstadt, a neighbourhood of the 19th district of Vienna, Dobling.

Karl Marx-Hof was built between 1927 and 1930 by city planner Karl Ehn, a follower of Otto Wagner. It held 1,382 apartments (with a size of 30-60 m2 each) and was called the Ringstrasse des Proletariats, the Ring-road of the Proletariat. (Vienna's principal Ringstrasse, dating from the 1850s, surrounds the city centre and had been intended as a showcase for the grandeur and glory of the Habsburg Empire). Only 18.5% of the 1,000 metres long, 156,000-m2 large area was built up, with the rest of the area developed into play areas and gardens. Designed for a population of about 5,000, the premises include many amenities, including laundromats, baths, kindergartens, a library, doctor offices, and business offices.

The heavy artillery damage to Karl Marx-Hof was repaired in the 1950s. It has been used as a filming location for some movies, most notably The Night Porter. The building was refurbished between 1989 and 1992. At over one kilometre in length (1100m, 0.68 mile) and spanning four Strassenbahn (tram) stops, Karl Marx-Hof holds the distinction of being the longest single residential building in the world.