刺刀，又称铳剑、铳刀，为安装或捆绑在枪管上的匕首、小刀式武器，作为远距武器的近距离防御使用。

刺刀大约16世纪即出现，其英文名称来自17世纪法国巴约讷（Bayonne）的一场农民争执中。当时的农民将小刀插入来福枪枪口内，用以袭击敌人。此发明便以出现地命名为「Bayonet」。在远东地区，根据明代书籍《兵录》内容，子母鸟铳附有塞管式铳刀一把。。

当时已经组成了使用火枪的枪兵队，而因为火枪为单发射击之故，在射击与射击间容易受到敌方步兵与骑兵的突击，在面对突击时仅有剑做为武器的火枪兵太过于无力。因此当时的火枪兵身旁常有手持长枪的枪兵负责保护。而装备刺刀的火枪兵将可以单独面对敌方的步兵与骑兵，得以挪出空间将枪兵训练为火枪兵，编制出全员皆为火枪兵的部队，大幅提升战力。

A knife bayonet is a knife which can be used both as a bayonet, fighting or utility knife. The knife bayonet became the almost universal form of bayonet in the 20th century due to its versatility and effectiveness. Spike bayonets proved useless when separated from the rifle and useless in trench warfare; and while versatile, sword bayonets proved to be impractical weapons in trench warfare because of their length. The first knife bayonet to see widespread service was the 10 inch blade Seitengewehr 1871/84, which became the standard German infantry bayonet in 1884. Its derivative, the Seitengewehr 1884/98, would go on in use until 1945 in German service.