Leo William Goossen (7 June 1892 – 4 December 1974) was a draftsman, mechanical engineer and automobile designer. He is known for his work with Harry Miller and his long involvement in the design and ongoing development of the four-cylinder Offenhauser ("Offy") racing engine. Goossen is considered to have been the preeminent American designer of racing engines over a fifty-year period that began in the early 1920s.