The Order of Saint Stephen is a Roman Catholic Tuscan dynastic military order founded in 1561. The order was created by Cosimo I de' Medici, first Grand Duke of Tuscany. The last member of the Medici dynasty to be a leader of the order was Gian Gastone de Medici in 1737. The order was permanently abolished in 1859 by the annexation of Tuscany to the Kingdom of Sardinia. The former Kingdom of Italy and the current Italian Republic also did not recognize the order as a legal entity but tolerates it as a private body.

A military order is a Christian religious society of knights. The original military orders were the Knights Templar, the Knights Hospitaller, the Order of Saint James, the Order of Calatrava, and the Teutonic Knights. They arose in the Middle Ages in association with the Crusades, both in the Holy Land, the Baltics, and the Iberian peninsula; their members being dedicated to the protection of pilgrims and Christians, as well as the defence of the Crusader states. They are the predecessors of chivalric orders.