In many rites of the Roman Catholic Church and in Anglican churches, a diocese is an administrative territorial unit administered by a bishop. It is also referred to as a bishopric or Episcopal Area (as in United Methodism) or episcopal see, though strictly the term episcopal see refers to the domain of ecclesiastical authority officially held by the bishop, and bishopric to the post of being bishop. The diocese is the key geographical unit of authority in the form of church governance known as episcopal polity. In the Roman Catholic Church and the Anglican Communion, an important diocese is called an archdiocese (usually due to size, historical significance, or both), which is governed by an archbishop, who may be exempt from or have metropolitan authority over the other ('suffragan') dioceses within a wider jurisdiction called an ecclesiastical province.
As of January 2009, there are 630 Roman Catholic archdioceses (including 13 patriarchates, 2 catholicates, 536 metropolitan archdioceses, 79 single archdioceses) and 2,167 dioceses in the world. After the Reformation, the Church of England continued and developed the existing diocesan structure in England. This continued throughout the Anglican Communion. In the Eastern Catholic Churches (which recognise papal authority and so are in communion with the Roman Catholic Church), the equivalent unit is called an eparchy; the Orthodox Church calls its dioceses metropoleis in the Greek tradition, Slavic tradition calls their dioceses eparchies.
See also: Bishops and civil governmentIn 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").
With the adoption of Christianity as the Empire's official religion in the 4th century, the clergy assumed official positions of authority alongside the civil governors. A formal church hierarchy was set up, parallel to the civil administration, whose areas of responsibility often coincided. With the collapse of the Western Empire in the 5th century, the bishops in Western Europe assumed a large part of the role of the former Roman governors. A similar, though less pronounced, development occurred in the East, where the Roman administrative apparatus was largely retained by the Byzantine Empire. In modern times, many an ancient diocese, though later divided among several dioceses, has preserved the boundaries of a long-vanished Roman administrative division. For Gaul, Bruce Eagles has observed that "it has long been an academic commonplace in France that the medieval dioceses, and their constituent pagi, were the direct territorial successors of the Roman civitates.
Modern usage of 'diocese' tends to refer to the sphere of a bishop's jurisdiction. This became commonplace during the self-conscious "classicizing" structural evolution of the Carolingian empire in the 9th century, but this usage had itself been evolving from the much earlier parochia ("parish"), dating from the increasingly formalised Christian authority structure in the 4th century (see EB 1911).
In the Methodist Church (Covering Great Britain and Ireland), churches are grouped together in sections. Sections are grouped together to form Circuits. Circuits are grouped together to form Districts. All of these, combined with the local membership of the Church, are referred to as the 'Connexion'. This, 18th century term, endorsed by John Wesley describes how people serving in different geographical centres are 'connected' to each other. The Methodist Church has an annual president. Each District is headed by a 'Chair' who oversees its functioning. Each Circuit is governed by a superintendent minister. The geographical regions covered by circuits and dioceses rarely overlap.
In the United Methodist Church (USA), a bishop is given oversight over a geographical area called an Episcopal Area. Each episcopal area contains one or more annual conference, which is how the churches and clergy under the bishop's supervision are organized. Thus, the use of the term "diocese" referring to geography is the most equivalent in the United Methodist Church, whereas each annual conference is part of one episcopal area (though that area may contain more than one conference). The African Methodist Episcopal Church shares a similar structure of the United Methodist Church, also using the Episcopal Area.
In the Church of Jesus Christ of Latter-day Saints, a bishop is not the leader of a large administrative area, but is rather the spiritual leader of an individual local congregation (known as a ward and roughly equivalent to a Catholic parish). A stake is the rough equivalent of a diocese.