The Arado Ar 66 was a German single-engined, two-seat training biplane, developed in 1933. It was also used for night ground-attack missions on the Eastern Front. It was engineer Walter Rethel's last design in collaboration with Arado, before Walter Blume, assigned as Arado Flugzeugwerke's chief design engineer in 1933, took over the bulk of the Arado firm's design duties.