The Rapp 100 hp was a four-cylinder, SOHC valvetrain liquid-cooled inline aircraft engine built by Rapp Motorenwerke. The engine originated from Karl Rapp's earlier 90 hp four-cylinder that he had designed at the Flugwerk Deutschland GmbH for the 1912/13 Kaiserpreis aircraft engine contest.

Rapp Motorenwerke GmbH was a German aircraft engine manufacturer based in Munich, Bavaria. Founded in 1913, the firm changed its name in 1917 to Bayerische Motoren Werke GmbH (BMW). The company later became known as Süddeutsche Bremsen-AG after its engine-production assets and the BMW name were transferred in 1922 to Bayerische Flugzeugwerke, which was then renamed to Bayerische Motoren Werke AG and subsequently evolved into the automotive manufacturer known today as BMW.