The Matter of Britain (matière de Bretagne) is the body of medieval literature and legendary material associated with Great Britain and Brittany and the legendary kings and heroes associated with it, particularly King Arthur. It was one of the three great Western story cycles recalled repeatedly in medieval literature, together with the Matter of France, which concerned the legends of Charlemagne, and the Matter of Rome, which included material derived from or inspired by classical mythology. Its pseudo-chronicle and chivalric romance works, written both in prose and verse, flourished from the 12th to the 16th century, particularly in northern France.
The three "matters" were first described in the 12th century by French poet Jean Bodel, whose epic La Chanson des Saisnes [fr] ("Song of the Saxons") contains the lines:
The name distinguishes and relates the Matter of Britain from the mythological themes taken from classical antiquity, the "Matter of Rome", and the tales of the Paladins of Charlemagne and their wars with the Moors and Saracens, which constituted the "Matter of France".
King Arthur is the chief subject of the Matter of Britain, along with stories related to the legendary kings of Britain, as well as lesser-known topics related to the history of Great Britain and Brittany, such as the stories of Brutus of Troy, Coel Hen, Leir of Britain (King Lear), and Gogmagog.
The legendary history of Britain was created partly to form a body of patriotic myth for the country. Several agendas thus can be seen in this body of literature. According to John J. Davenport, the question of Britain's identity and significance in the world "was a theme of special importance for writers trying to find unity in the mixture of their land's Celtic, Anglo-Saxon, Roman and Norse inheritance."
Geoffrey of Monmouth's Historia Regum Britanniae is a central component of the Matter of Britain. Geoffrey drew on a number of ancient British texts, including the ninth century Historia Brittonum.