The Bishopric of Pomesania (German: Bistum Pomesanien; Polish: Diecezja pomezańska) was a Catholic diocese in the Prussian regions of Pomesania and Pogesania, in northern modern Poland until the 16th century, then shortly a Lutheran diocese, and became a Latin titular see.
It was founded as one of four Roman Catholic dioceses in Prussia in 1243 by the papal legate William of Modena.
The bishops, whose seat was Riesenburg (Prabuty), ruled one third of diocesan territory as his temporality. The diocesan cathedral chapter met in the fortified cathedral of Marienwerder (Kwidzyn). In the 1280s the Teutonic Order succeeded to impose the simultaneous membership of all capitular canons in the Order thus winning influence in the diocese and in the capitular elections of the bishops. So the temporality of Pomesania's bishop did not develop the status of a prince-bishopric and was ruled as part of Teutonic Prussia.
Beginning in 1523 during the Protestant Reformation, the diocese was effectively administered by Lutheran bishops until 1587, when the diocese was secularized by the regent of Ducal Prussia, George Frederick.