The Piaggio P.X, or Piaggio Stella P.X, was an Italian nine-cylinder radial aircraft engine produced by Rinaldo Piaggio S.p.A. Based on experience license-producing Gnome et Rhône designs, the engine was used to power a number of aircraft during World War II, including the IMAM Ro.37bis and IMAM Ro.43, used extensively by the Regia Aeronautica and Regia Marina respectively.

Piaggio acquired a license from Gnome et Rhône in 1925 for their engines derived from the Bristol Jupiter.

[1] The designs proved successful and, using this experience, the company designed a range of related radial engines named "Stella", meaning star.

[3] The engines were initially known by their number of cylinders, so the first nine-cylinder model in the range was the P.IX of 1933.

[2] The engine powered the Italian aircraft that served during World War II.