自动步枪指自动进弹、连续击发、具备全自动射击能力的步枪。利用推进弹头的部分气体或后座力进行退弹壳、装弹并再次射击的步枪，也就是说，只要扣住扳机不放，就能连续射击，直到枪内子弹用尽。

自动步枪包括了制式自动步枪、重管自动步枪和突击步枪。

自20世纪初俄国的费德洛夫M1916自动步枪、法国的Mle 1918 全自动卡宾枪以及第一次世界大战后出现的白朗宁自动步枪。到第二次世界大战中出现的StG44突击步枪，以后至60年代，枪械自动化结构迅速发展。先后有前苏联米哈伊尔·卡拉什尼科夫研制的AK-47突击步枪，美国人研制的M16突击步枪等。

An automatic rifle is a type of magazine-fed rifle that uses either its recoil or a portion of the gas propelling the projectile to remove the spent cartridge case, cock the rifle, load a new cartridge and fire again repeatedly, as long as the trigger is held down or until the magazine is exhausted. Automatic rifles are distinguished from semi-automatic rifles in their ability to fire more than one shot in succession once the trigger is pulled. Many automatic rifles are select-fire weapons which are capable of firing in fully automatic and semi-automatic modes, or in some cases, even being capable of burst-fire.