The Lockheed XF-104 was a single-engine, high-performance, supersonic interceptor prototype for a United States Air Force (USAF) series of lightweight and simple fighters. Only two aircraft were built, one aircraft was used primarily for aerodynamic research and the other served as an armament testbed. Both prototypes were destroyed in accidents during testing. The XF-104 was the forerunner of over 2,500 Lockheed F-104 Starfighters.

During the Korean War, USAF fighter pilots were outclassed by MiG-equipped Soviet pilots. Lockheed engineers, led by Kelly Johnson, designed and submitted a novel design to the Air Force. The design was notable for its sleekness, particularly its thin wings and missile-shaped fuselage, as well as a novel pilot ejection system.

The XF-104's maiden flight came in February 1954. The flight test program encountered problems, some of which were resolved; however, the XF-104 performance proved better than estimates. Both prototypes were lost through accidents. Nevertheless, the USAF ordered 17 service-test F-104s. Internationally, the production F-104 Starfighters proved popular, serving as front-line fighters with a number of countries.