The Diocese of Ratzeburg (German: Bistum Ratzeburg, Latin: Dioecesis Ratzeburgensis) is a former diocese of the Catholic Church. It was erected from the Diocese of Oldenburg c. 1050 and was suppressed in 1554.[1] The diocese was originally a suffragan of the Archdiocese of Hamburg; in 1072 it became a suffragan of the merged entity — the "Archdiocese of Hamburg and the Diocese of Bremen". The territory of the diocese was located in what is today the states of Schleswig-Holstein (the district of Herzogtum Lauenburg) and Mecklenburg-Vorpommern (the district of Nordwestmecklenburg) in Germany. The cathedral church of the diocese — dedicated to Ss. Mary and John — is still extant in the city of Ratzeburg. Following its suppression as part of the Protestant Reformation, the remaining Catholic adherents were only represented by the Apostolic Vicariate of Northern Germany. The whole territory of the diocese is today included in the Roman Catholic Archdiocese of Hamburg.