Heckler & Koch GmbH (HK) is a German defense manufacturing company that manufactures handguns, assault rifles, submachine guns, and grenade launchers. The company is located in Oberndorf in the state of Baden-Württemberg, and also has subsidiaries in the United Kingdom, France and the United States.

The Heckler & Koch Group comprises Heckler & Koch GmbH, Heckler & Koch Defense, NSAF Ltd., and Heckler & Koch France SAS. The company's motto is "Keine Kompromisse!" (No Compromises!). HK provides firearms for many military and paramilitary units, like the SAS, KMar, the US Navy SEALs, Delta Force, HRT, Canada's Joint Task Force 2, the German KSK and GSG 9 and many other counter-terrorist and hostage rescue teams.

Some of their more notable products include the MP5, UMP submachine guns, the G3, HK417 battle rifles, the HK33, G36, HK416 assault rifles, the MG5, HK21 General-purpose machine guns, the MP7 personal defense weapon, the USP series of handguns, and the high-precision PSG1 sniper rifle. All HK firearms 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 its technologically ambitious designs have become commercially successful products (for instance, the advanced but now abandoned G11 military rifle, which fired caseless high-velocity ammunition). In its extensive product range, HK has used the following operating systems for small arms: blowback operation, short-recoil, roller-delayed blowback, gas-delayed blowback, and gas operation (via Short-stroke piston).