The Ducati 900 is a series of air-cooled, two-valve, V-twin motorcycle engines produced by Ducati since the 1980s. The 900cc engine was available in several different variants, most of which are no longer in production. The engines have been used in a variety of Ducati motorcycles, including the 900SS, 748, 916, and 996. The Ducati 900 was a popular choice for professional and amateur racers, and the engines powered several world championship-winning bikes.