Military Frontier (Military Border, Military Krajina, Vojna Krajina, Militärgrenze, Confiniaria militaria) was a borderland of Habsburg Austria which acted as the cordon sanitaire against the Turks from the Middle Ages (Croatian Krajina) or from the late 1600s (Slavonian and Banat Krajina) until the 19th century.

The border areas were separated from their crownlands into the Military Frontier in 1553 and 1578, which was divided into the following districts:

• Banat Krajina (on the Serbian-Romanian border)
• Slavonian Krajina (on the border of Vojvodina and Eastern Croatia towards Bosnia)
• Croatian Krajina (on the border of Western Croatia and Bosnia)

Due to the constant border wars, the area became rather depopulated, and the authorities encouraged immigration of various peoples. The majority of settlers were Serbs and Vlachs who came from territories in the southeast, fleeing the Turkish occupation. Germans and Magyars mostly came as administrative personnel, and there was a number of other settlers and military persons from other parts of the Austrian Empire such as the Czechs, Slovaks, Ukrainians/Rusyns and others.

The military rule from Vienna remained in place until 1869 when the demilitarization started, ending in 1871 when Franz Joseph abolished the Frontier.

The areas of Slavonian and Croatian Krajina later formed the Republic of Serbian Krajina in the 1990s during the Yugoslav wars. The Banat Krajina was unaffected by this.