Festung Rüsselsheim, Medieval fortress in Rüsselsheim am Main, Germany.

Festung Rüsselsheim is a former defensive complex in Rüsselsheim am Main, built from 1479 under Heinrich III of Hesse with ramparts, moats and five bastions. The grounds now house the Stadt- und Industriemuseum Rüsselsheim, founded in 1976, along with the city archive and a café.

A castle of the Counts of Katzenelnbogen was first documented in 1399. From 1479, after Rüsselsheim passed to Hesse under Heinrich III, it was rebuilt as a fortress with ramparts, ditches and five bastions, completed by 1546. Philipp the Magnanimous surrendered it to Emperor Charles V in 1547; it was demolished, then rebuilt in 1560–1563. French troops blew it up on 6 April 1689.

The Stadt- und Industriemuseum Rüsselsheim, founded in 1976, has occupied the fortress since the 1970s and received a Council of Europe museum prize in 1979. The city archive, a café and the local heritage association (Heimatverein) are also based here, and a regular arts and crafts market is held on the grounds.

The fortress was bought by the city of Rüsselsheim in 1954 and has been open to the public since then; it has been restored in keeping with its listed status since the 1990s. The Stadt- und Industriemuseum, the town archive, a café and the local heritage association are housed on the grounds. The museum is closed on Mondays.

The fortress ruins served as a prison, a military hospital, a mushroom farm and a youth hostel before the city bought the site in 1954 and opened it to the public.