The Livonian Brothers of the Sword or Livonian Order was a military order organized in 1202 by Albert of Buxhoeveden and composed of German "warrior monks". Their rule was primarily based on that of the Knights Templar. They were also known as the Christ Knights, Sword Brethren, and The Militia of Christ of Livonia.

Their names in different languages include:

Latin: Fratres miliciae Christi de Livonia, "Brothers of the Army of Christ of Livonia"

, "Order of Sword-brothers"

or Liivimaa Ordu, "Livonian Order"

and Livonijas ordenis, "Livonian Order"

, "Order of the Brothers of the Sword"

Albert, bishop of Riga (or Prince-Bishop of Livonia), founded the Brotherhood to aid the Bishopric of Riga in the conversion of the pagan Curonians, Livonians, Semigallians, and Latgalians along the Gulf of Riga. From its foundation the undisciplined Order tended to ignore its supposed vassalage to the bishops. In 1218 Albert asked King Valdemar II of Denmark for assistance, but Valdemar instead arranged a deal with the Brotherhood and conquered the north of Estonia.

The Brotherhood's headquarters were at Fellin (Viljandi) in Estonia, where the walls of the master's castle are still standing. Other strongholds included Wenden (Cēsis), Segewold (Sigulda) and Ascheraden (Aizkraukle). The commanders of Fellin, Goldingen (Kuldīga), Marienburg (Alūksne), Reval (Tallinn), and the bailiff of Weißenstein (Paide) belonged to the five-member entourage of the Order's master.

The Brothers were all but annihilated by the Lithuanians and Semigallians at the Battle of Schaulen/Saule in 1236. In the following year, however, the Brotherhood was incorporated into the Order of Teutonic Knights. From that point on, they were in all respects (rule, clothing and policy) an autonomous branch of the Teutonic Order, headed by their own Master (who was de jure subject to the Teutonic Order's Grand Master). Between 1237 and 1290 they conquered all of Courland, Livonia and Semigallia. In 1346 the Order bought the rest of Estonia and the possessions of the Blue order from King Valdemar IV of Denmark. Life within the Order's territory is described in the Chronicle of Henry of Livonia and the Livonian Rhymed Chronicle.

The Teutonic Order fell into decline following its defeat in the Battle of Grunwald in 1410 and the secularization of its Prussian territories by Albert of Prussia in 1525, but the Livonian Order managed to maintain an independent existence. During the Livonian War, however, they suffered a decisive defeat by troops of Muscovite Russia in the Battle of Ergeme in 1560. The Livonian Order then sought protection from King Sigismund II Augustus of Poland, who had intervened in a war between Bishop William of Riga and the Brothers in 1557.

After coming to an agreement with the Polish king and his representatives (especially Mikołaj "Czarny" Radziwiłł), the last Master, Gotthard Kettler, secularized the Order and converted to Lutheranism. In the southern part of the Brothers' lands he created the Duchy of Courland and Semigallia for his family. Most of the remaining lands were seized by the Polish-Lithuanian Commonwealth. The north of Estonia was taken back by Denmark and Sweden.