The Knights of the Round Table (Welsh: Marchogion y Ford Gron, Cornish: Marghekyon an Moos Krenn, Breton: Marc'hegien an Daol Grenn) are the legendary knights of the fellowship of King Arthur that first appeared in the Matter of Britain literature in the mid-12th century. The Knights are an order dedicated to ensuring the peace of Arthur's kingdom following an early warring period, entrusted in later years to undergo a mystical quest for the Holy Grail. The Round Table at which they meet is a symbol of the equality of its members, who range from sovereign royals to minor nobles.

The various Round Table stories present an assortment of knights from all over Great Britain and abroad, some of whom are even from outside of Europe. Their ranks often include Arthur's close and distant relatives, as in the cases of Agravain, Gaheris and Yvain, as well as his reconciled former enemies, like Galehaut, Pellinore and Lot. Several of the most notable Knights of the Round Table, among them Bedivere, Gawain and Kay, are based on older characters from a host of great warriors associated with Arthur in the early Welsh tales. Some, such as Lancelot, Perceval and Tristan, feature in the roles of a protagonist or eponymous hero in various works of chivalric romance. Other well-known members of the Round Table include the holy knight Galahad, replacing Perceval as the main Grail Knight in the later stories, and Arthur's traitorous son and nemesis Mordred.

By the end of Arthurian prose cycles (including the seminal Le Morte d'Arthur), the Round Table splits up into groups of warring factions following the revelation of Lancelot's adultery with King Arthur's wife, Queen Guinevere. In the same tradition, Guinevere is featured with her own personal order of young knights, known as the Queen's Knights. Some of these romances retell the story of the Knights of the Old Table, led by Arthur's father, Uther Pendragon, whilst other tales focus on the members of the 'Grail Table'; these were the followers of ancient Christian Joseph of Arimathea, with his Grail Table later serving as the inspiration for Uther and Arthur's subsequent Round Tables.