The Combat of the Thirty (French: Combat des Trente, Breton: Emgann an Tregont), occurring on 26 March 1351, was an episode in the Breton War of Succession fought to determine who would rule the Duchy of Brittany. It was an arranged fight between selected combatants from both sides of the conflict, fought at a site midway between the Breton castles of Josselin and Ploërmel among 30 champions, knights, and squires on each side. The challenge was issued by Jean de Beaumanoir, a captain of Charles of Blois supported by King Philip VI of France, to Robert Bemborough, a captain of Jean de Montfort supported by Edward III of England.

After a hard-fought battle, the Franco-Breton Blois faction emerged victorious. The combat was later celebrated by medieval chroniclers and balladeers as a noble display of the ideals of chivalry. In the words of Jean Froissart, the warriors "held themselves as valiantly on both sides as if they had been all Rolands and Olivers".