骑士或称武士，是欧洲中世纪时，受过正规军事训练的骑兵，后来演变为一种荣誉称号，用于表示一种社会阶层。在此阶段的纷乱局势中，国王和贵族都需要一些在战争上具有压倒性优势的兵种，因此具有优于步兵的机动力的骑士就成为战争中的主力，并逐渐成为贵族阶级中的一部份。骑士此一头衔与领主身分有所差异，并不是继承而来的，而是来自另一位骑士或是高端领主的册封，除了和领主一样能够从君主那获得封地之外，骑士必须在领主的军队中服役，并在战争时自备武器与马匹。在今日的部分欧洲国家则保留有纯为荣誉头衔的骑士称号。

虽然不一定与现实相同，但在骑士文学中，骑士往往是勇敢、忠诚的象征，每一位骑士都以骑士精神作为守则，是英雄的化身，欧洲的骑士制度和日本的武士制度亦有相似。

A knight (/naɪt/) is a person granted an honorary title of knighthood by a monarch or other political leader for service to the Monarch or country, especially in a military capacity. Historically, in Europe, knighthood has been conferred upon mounted warriors. During the High Middle Ages, knighthood was considered a class of lower nobility. By the Late Middle Ages, the rank had become associated with the ideals of chivalry, a code of conduct for the perfect courtly Christian warrior. Often, a knight was a vassal who served as a fighter for a lord, with payment in the form of land holdings and food from serfs. The lords trusted the knights, who were skilled in battle on horseback. Since the early modern period, the title of knight is purely honorific, usually bestowed by a monarch, as in the British honours system, often for non-military service to the country. The modern female equivalent is Dame.