The ArmaLite AR-15 (the "AR" is an acronym for "ArmaLite Rifle") is a select-fire, air-cooled, gas-operated, magazine-fed rifle manufactured in the United States between 1959 and 1964.Designed by American gun manufacturer ArmaLite in 1956, it was based on its AR-10 rifle. The ArmaLite AR-15 was designed to be a lightweight rifle and to fire a new high-velocity, lightweight, small-caliber cartridge to allow infantrymen to carry more ammunition.

In 1959, ArmaLite sold its rights to the AR-15 to Colt due to financial difficulties and limitations in terms of manpower and production capacity. After modifications (most notably, the charging handle was re-located from under the carrying handle like AR-10 to the rear of the receiver), Colt rebranded it the Colt 601, however it still carried the Armalite markings due to contractual obligations to Armalite/Fairchild Aircraft Co.. Colt marketed the redesigned rifle to various military services around the world and was eventually adopted by the U.S. military in January 1962 and subsequently designated as M16 rifle in December 1963, which went into production and service in 1964.

Colt continued to use the AR-15 trademark for its line of semi-automatic-only rifles marketed to civilian and law-enforcement customers, known as Colt AR-15. The Armalite AR-15 is the parent of a variety of Colt AR-15 and M16 rifle variants.