This article is about ecclesiastical dioceses. For the administrative unit in the Roman Empire, see Roman diocese.
In some Christian churches, the diocese is an administrative territorial unit administrated by a bishop, hence also referred to as a bishopric or Episcopal Area (as in United Methodism) or episcopal see, though more often the term episcopal see means the office held by the bishop. The diocese is the key unit of authority in the form of church governance known as episcopal polity. In the Roman Catholic Church, an important diocese is called an archdiocese (usually due to size, historical significance, or both), which is governed by an Archbishop, who may in the Catholic hierarchy either be exempt from or have Metropolitan authority over the other ('suffragan') dioceses within a wider jurisdiction called ecclesiastical province. As of 2003, there are approximately 569 Roman Catholic archdioceses and 2014 dioceses.
The Orthodox Church calls its dioceses Metropolises.
The Church of England continued and developed this diocesan structure after the Reformation.
In the later organization of the Roman Empire, the increasingly subdivided provinces were administratively associated in a larger unit, the diocese. (Latin dioecesis, from the Greek term διοίκησις meaning "administration").
The Catholic Church adopted the Roman diocesan structure of authority during the 5th and 6th centuries, as each bishop fully assumed the role of the former Roman praefectus. This transfer of authority from secular officials to ecclesiastical leaders was facilitated by the Christian practice of establishing areas of ecclesiastical administration that coincided with those of the Roman civil administration. In modern times, many an ancient diocese, though later divided among several dioceses, has preserved the boundaries of a long-vanished Roman administrative division. See also: Bishops and civil government.

Other denominations

List of Anglican Church of Canada dioceses
List of Church of England dioceses
List of Church of Ireland dioceses
Dioceses of the Episcopal Church in the United States of America
List of the dioceses of the Orthodox Church in America
List of Roman Catholic archdioceses
List of Roman Catholic dioceses
Eparchy, a term in Eastern Catholicism, Eastern Orthodoxy, Oriental Orthodoxy, and the Assyrian Church of the East
Stake, a term in Mormonism
List of Bishops
Particular Church
Ecclesiastical Latin
Catholic Church in Great Britain
How the Church of England is organised