The Heinkel He 51 was a German single-seat biplane fighter aircraft. A seaplane variant and a ground-attack version were also developed. It was a development of the earlier He 49.

Heinkel Flugzeugwerke was a German aircraft manufacturing company founded by and named after Ernst Heinkel. It is noted for producing bomber aircraft for the Luftwaffe in World War II and for important contributions to high-speed flight, with the pioneering examples of a successful liquid-fueled rocket and a turbojet-powered aircraft in aviation history, with both Heinkel designs' first flights occurring shortly before the outbreak of World War II in Europe.