The Diocese of Mondoñedo-Ferrol is a Latin diocese of the Catholic Church in Spain. It is the northernmost of the four suffragan dioceses in the ecclesiastical province of the Metropolitan Archdiocese of Santiago de Compostela, which covers Galicia in the northwest of Spain. The area had previously been home to Britonia, a settlement founded by expatriate Britons in the wake of the Anglo-Saxon invasion of Britain. Britonia was represented by the diocese referred to as Britonensis ecclesia in sources from the 6th and 7th centuries.