The Duchy of Saint Sava[1][2][3][4][5][6][7] (Serbo-Croatian: Vojvodstvo Svetog Save, Војводство Светог Саве)[a] was a late medieval polity in southeastern Europe, that existed from 1448 up to 1482, when it was absorbed by the Ottoman Empire.

It was founded and controlled by the Kosača noble family, whose rulers held the title Duke of Saint Sava (Serbo-Croatian: Herceg od Svetog Save, Херцег од Светог Саве).

Since 1435, the family was headed by Stjepan Vukčić Kosača, a mighty feudal lord and veliki vojvoda of Bosnia, whose relations with Bosnian kings became turbulent, due to his high ambitions.

[49] Stjepan also improved his relations with the Serbian Despot Đurađ Branković, and already in 1448-1449 they formed an alliance, and conquered Višegrad and Srebrenica from the Bosnian crown.

In the royal charter, Stjepan was addressed as: "illustris Stephani ducis Sancte Save Domini terre Hulminis maritimarum partium ac comiti Drine et magni vayvode Regni Boccine".

[55][56][57] Religious situation in Stjepan's domains was complex,[58] since his subjects belonged to three Christian denominations (Eastern Orthodoxy, Roman Catholicism, and the Bosnian Church).

[59] Prominent members of his court were metropolitan David of Mileševa (of the Serbian Patriarchate of Peć), and gost Radin (of the Bosnian Church).

[60][61][62] Ethnic composition of Stjepan's wast domains was also complex, encompassing local South Slavic populations, and also romance Vlachs.

As a result of Ottoman expansion during the previous years, territory of the formerly wast Duchy of Saint Sava was gradually reduced to its southeastern regions around Novi.

In order to demonstrate clemency, sultan granted some inland possessions to duke Vlatko, who lived under Ottoman rule for several years, but later moved under Venetian protection and settled in the island of Rab.