The Heckler & Koch MP5 (from German: Maschinenpistole 5, "machine pistol model 5") is a 9mm submachine gun of German design, developed in the 1960s by a team of engineers from the German small arms manufacturer Heckler & Koch GmbH (H&K) of Oberndorf am Neckar.

The MP5 is currently one of the most widely used submachine guns in the world, having been adopted by numerous military, law enforcement, intelligence, and security organizations. In the 1990s, Heckler & Koch developed the Heckler & Koch UMP, the MP5's successor, though both remain in production.

Heckler & Koch, encouraged by the success of the G3 automatic rifle, developed a family of small arms consisting of four types of firearms (all based on a common G3 design layout and operating principle), where the first type was chambered in 7.62x51mm NATO, the second—using the 7.62x39mm M43 round, third—the intermediate 5.56x45mm NATO caliber and the fourth type—chambering the 9x19mm Parabellum pistol cartridge. The MP5 was created within the fourth group of firearms and was initially known as the HK54.

Heckler & Koch GmbH (HK) (German pronunciation: [ˈhɛklɐʔʊntˈkɔx]) is a German defense manufacturing company that produces various small arms. Some of their products include the MP5 submachine gun, G3 automatic rifle, the G36 assault rifle, the HK 416, the MP7 personal defense weapon, the USP series of handguns, and the high-precision PSG1 sniper rifle. All firearms made by HK are named by a prefix and the official designation, with suffixes used for variants.

HK has a history of innovation in firearms, such as the use of polymers in weapon designs and the use of an integral rail for flashlights on handguns. HK also developed modern polygonal rifling, noted for its high accuracy, increased muzzle velocity and barrel life. Not all of its technologically ambitious designs have translated into commercially successful products (for instance, the advanced but now abandoned G11 assault rifle, which fired caseless high-velocity ammunition). HK produces a whole range of small arms, from pistols to grenade launchers and machine guns. In its extensive product range, HK has used most of the operating systems for small arms: blowback operation, short-recoil, roller-delayed blowback, gas-delayed blowback, and gas operation.