The Hildesheim Diocesan Feud or Great Diocesan Feud, sometimes referred to as a "chapter feud", was a conflict that broke out in 1519 between the Prince-Bishopric of Hildesheim and the principalities of Brunswick-Wolfenbüttel and Calenberg that were ruled by the House of Welf. Originally just a local conflict between the Hildesheim prince-bishop John IV of Saxe-Lauenburg and his own prince-bishopric's nobility (Stiftsadel), it developed into a major dispute between various Lower Saxon territorial princes. The cause was the attempt by Prince-Bishop John to redeem the pledged estates and their tax revenue from the nobles in his temporalities, the prince-bishopric. The diocesan feud ended with the Treaty of Quedlinburg in 1523.

The Prince-Bishopric of Hildesheim was an ecclesiastical principality of the Holy Roman Empire from the Middle Ages until its dissolution in 1803. The Prince-Bishopric must not be confused with the Diocese of Hildesheim, which was larger and over which the prince-bishop exercised only the spiritual authority of an ordinary bishop.