The Catholic dioceses in Great Britain are organised by two separate hierarchies: the Catholic Church in England and Wales, and the Catholic Church in Scotland. Within Great Britain, the Catholic Church in England and Wales has five provinces, subdivided into 21 dioceses, and the Catholic Church in Scotland has two provinces, subdivided into 8 dioceses. The Catholic dioceses in Northern Ireland are organised together with those in the Republic of Ireland, as the Catholic Church in Ireland was not divided when civil authority in Ireland was partitioned in 1921.
A diocese, also sometimes known popularly as a bishopric, is an administrative unit under the supervision of a bishop.