The Prince-Bishopric of Warmia is a semi independent ecclesiastical state, ruled by the incumbent ordinary of the Ermland/Warmia see and comprising one third of the then diocesan area.

The other two thirds of the diocese are under the secular rule of the Monastic state of the Teutonic Knights (Teutonic Prussia) (until 1525, and Ducal Prussia hereafter).

The Ermland/Warmia see is a Prussian diocese under the jurisdiction of the Archbishopric of Riga that is a protectorate of Teutonic Prussia (1243–1466) and a protectorate of Kingdom of Poland, later part of the Polish-Lithuanian Commonwealth after the Peace of Thorn (1466–1772).Originally founded as the Bishopric of Ermland, it is created by William of Modena in 1243 in the territory of Prussia after its conquest by the Teutonic Knights during the Northern Crusades.

The diocesan cathedral chapter is constituted in 1260.

While in the 1280s the Teutonic Order succeeds in imposing the simultaneous membership of all capitular canons in the Order in the other three Prussian bishoprics, Ermland's chapter maintains its independence and is therefore able to repel outside influence when electing its bishops.

Thus the Golden Bull of Emperor Charles IV names the bishops as prince-bishops, a rank not awarded to the other three Prussian bishops (Culm, Pomesania, and Samland).

By the Second Peace of Thorn (1466) the prince-bishopric—like other western areas of Teutonic Prussia—secedes and forms a part of Royal Prussia, which adopts the King of Poland as sovereign in a personal union.

After Royal Prussia joins the Polish-Lithuanian Commonwealth in 1569, Ermland's autonomy gradually fades.