A 5.56×45mm assault rifle, designed in the early 1990s by Heckler & Koch (H&K) in Germany as a replacement for the 7.62mm G3 battle rifle. It was accepted into service with the Bundeswehr in 1997, replacing the G3. The G36 is gas-operated and feeds from a 30-round detachable box magazine or 100-round C-Mag drum magazine.

Work on a successor for the venerable G3 rifle had been ongoing in Germany since the second half of the 1970s. These efforts resulted in the innovative 4.73mm G11 assault rifle (developed jointly by a group of companies led by H&K), that used caseless ammunition (designed by the Dynamit Nobel company). It had been predicted that this weapon would eventually replace the G3, therefore further development of H&K's series of firearms chambered for the 5.56x45mm NATO cartridge had been halted. Heckler & Koch, having no incentive to pursue a new 5.56mm weapon system, was content with the export-oriented HK33 and G41 rifles. However, the G11 programme came to an abrupt end when the Bundeswehr cancelled its procurement due to defence budget cuts after the unification of East and West Germany and H&K was acquired in 1991 by British Aerospace's Royal Ordnance division (known today as BAE Systems).

Increasing interest in Germany for a modern service rifle chambered for the NATO-standard 5.56mm cartridge led H&K to offer the German armed forces the G41 rifle, which, too, was rejected. Design work was then initiated from the ground up on a modern 5.56mm assault rifle designated "Project 50" or HK50. The prototype was then trialed, where it was rated higher than the rival Austrian Steyr AUG system.

The HK50 rifle was selected for service and an initial order was placed for 33,000 rifles under the Bundeswehr designation Gewehr G36. The order also involved an option for a further 17,000 rifles. Deliveries were first made to the Bundeswehr's NATO Quick Reaction Force during the third quarter of 1997.

In July 1998, it was announced that the G36 had been selected as the standard rifle for the Spanish Armed Forces, replacing the 5.56mm CETME Model L and LC rifles. Deliveries first took place at the end of 1999. These rifles are manufactured in Spain under licence by General Dynamics Santa Bárbara Sistemas at the FACOR (Fábrica de Armas de la Coruña) facility, in Corunna, Galicia.

In addition, the rifle has been licenced for local production in Saudi Arabia. The manufacturer in the country is the Military Industries Corporation.