The Knights Hospitaller, also known as the Hospitallers, Order of Hospitallers, Knights of St John, Order of St John, and currently The Sovereign Military Hospitaller Order of St. John of Jerusalem of Rhodes and of Malta, were among the most famous of the Western Christian military orders during the Middle Ages.

The Hospitallers arose as a group of individuals associated with an Amalfitan hospital in the Muristan district of Jerusalem, which was dedicated to St John the Baptist and was founded around 1023 by Blessed Gerard Thom to provide care for poor, sick or injured pilgrims to the Holy Land. Note that other sources claim the Amalfitan order and Amalfitan hospital were different from Gerard's order and its hospital. After the Western Christian conquest of Jerusalem in 1099 during the First Crusade, the organisation became a religious and military order under its own charter, and it was charged with the care and defence of the Holy Land. Following the conquest of the Holy Land by Islamic forces, the order operated from Rhodes, over which it was sovereign, and later from Malta where it administered a vassal state under the Spanish viceroy of Sicily.