The FN P90 is a personal defense weapon (PDW) designed and manufactured by FN Herstal in Belgium. Created in response to NATO requests for a replacement for 9×19mm Parabellum firearms, the P90 was designed as a compact but powerful firearm for vehicle crews, operators of crew-served weapons, support personnel, special forces and counter-terrorist groups.

Designed by FN in conjunction with the FN Five-seven pistol and FN 5.7×28mm ammunition, development of the weapon began in 1986, and production commenced in 1990 (from which the "90" in its name is derived), whereupon the 5.7×28mm ammunition was redesigned and shortened. A modified version of the P90 with a magazine adapted to use the new ammunition was introduced in 1993, and the Five-seven pistol was subsequently introduced as a companion weapon using the same 5.7×28mm ammunition.

Featuring a compact bullpup design with an integrated reflex sight and fully ambidextrous controls, the P90 is an unconventional weapon with a futuristic appearance. Its design incorporates several innovations such as a unique top-mounted magazine and FN's small-caliber, high-velocity 5.7×28mm ammunition.