The Barons' Crusade (1239–1241), also called the Crusade of 1239, was a crusade to the Holy Land that, in territorial terms, was the most successful crusade since the First Crusade. Called by Pope Gregory IX, the Barons' Crusade broadly embodied the highest point of papal endeavor "to make crusading a universal Christian undertaking." Gregory IX called for a crusade in France, England, and Hungary with different degrees of success. Although the crusaders did not achieve any glorious military victories, they used diplomacy to successfully play the two warring factions of the Ayyubid dynasty against one another for even more concessions than Frederick II had gained during the more well-known Sixth Crusade. For a few years, the Barons' Crusade returned the Kingdom of Jerusalem to its largest size since 1187.

Theobald I, also called the Troubadour and the Posthumous, was Count of Champagne from birth and King of Navarre from 1234. He initiated the Barons' Crusade, was famous as a trouvère, and was the first Frenchman to rule Navarre.