The Ninth Crusade is commonly considered to be the last of the medieval Crusades against the Muslims in the Holy Land.

Prince Edward of England had arrived in Tunis too late to contribute to Louis IX of France's Eighth Crusade, but along with Louis' brother Charles of Anjou he continued on to Acre, capital of the remnant of the Kingdom of Jerusalem. They arrived in 1271, just as the Mamluk sultan Baibars was unsuccessfully besieging Tripoli, the last remaining territory of the County of Tripoli. Earlier, in 1268, Baibars had also captured the Antioch, the last remnant of the Principality of Antioch.

Baibars also built the first Mamluk navy and attempted to land on Cyprus in 1271, drawing Hugh III of Cyprus (the nominal king of Jerusalem) out of Acre, but the fleet was destroyed. Edward did little except mediate between Hugh and his unenthusiastic knights from the Ibelin family of Cyprus, and negotiate an eleven-year truce with Baibars, although Baibars first attempted to assassinate him by sending men pretending to seek baptism as Christians. Edward returned home in 1272 when his father Henry III died.

Edward had been accompanied by Theobald Visconti, who became Pope Gregory X in 1271. Gregory called for a new crusade, especially at the Council of Lyons in 1274, but nothing came of this. Charles, however, took advantage of a dispute between Hugh III, the Knights Templar, and the Venetians in order to bring Acre states under his control. He bought Maria of Antioch's claims to the Kingdom of Jerusalem, and attacked Hugh III, who also claimed the kingdom. In 1277 Hugh of San Severino captured Acre for Charles.

Venice then suggested a crusade be called against Constantinople, where Michael VIII had recently re-established the Byzantine Empire. In 1281 Pope Martin IV gave permission for this; the French took the land route over Durazzo, while the Venetians took the sea route. However, after the Sicilian Vespers on March 31, 1282, instigated by Michael VIII, Charles was forced to return home.

This was the last expedition undertaken against the Byzantines or the Muslims in the east. By 1291 the Mameluks had captured the last of the Crusader territories.