The Diocese of Verden was a diocese of the Catholic Church. It was founded around AD 768 as a suffragan of the Archdiocese of Mainz. It was suppressed in 1648 as part of the Peace of Westphalia. The diocese was centered on the city of Verden an der Aller in what is today the state of Lower Saxony, Germany. The cathedral church of the diocese was dedicated to Ss Mary and Cecilia in 1028 but the building was only completed in 1490. The Bishop of Verden was also, ex officio, the ruler of a principality of the Holy Roman Empire — the Prince-Bishopric of Verden. The territory of the diocese was not identical with that of the prince-bishopric; while the state was located within the boundaries of the diocese, it amounted to less than a quarter of the diocesan territory. Its last bishop was Franz Wilhelm, Count von Wartenberg. Following the Thirty Years' War, Verden, along with the neighbouring sees of Minden and Bremen, fell into the hands of Protestants. Wartenberg was only able to retain the See of Osnabrück.

The Diocese of Hildesheim is a Latin Church diocese of the Catholic Church in Germany. Founded in 815 as a missionary diocese by King Louis the Pious, his son Louis the German appointed the famous former archbishop of Rheims, Ebbo, as bishop.