The Prince-Archbishopric of Bremen — not to be confused with the modern Archdiocese of Hamburg, founded in 1994 — was an ecclesiastical principality (787–1566/1648) of the Holy Roman Empire and the Catholic Church that after its definitive secularization in 1648 became the hereditary Duchy of Bremen. The prince-archbishopric, which was under the secular rule of the archbishop, consisted of about a third of the diocesan territory. The city of Bremen was de facto and de jure not part of the prince-archbishopric. Most of the prince-archbishopric lay rather in the area to the north of the city of Bremen, between the Weser and Elbe rivers. Even more confusingly, parts of the prince-archbishopric belonged in religious respect to the neighbouring Diocese of Verden, making up 10% of its diocesan territory.

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.