In the Roman Empire, a diocese was a city district or part of a province. In the Roman Catholic and some Protestant churches, a diocese is an administrative territorial unit governed by a bishop, sometimes also referred to as a bishopric or episcopal see (more often the term episcopal see means the office held by the bishop). An important diocese is called an archdiocese (usually due to size or historical significance). As of 2003, there are about 569 Roman Catholic archdioceses and 2014 dioceses in the world.
By the time of Diocletian it was a large administrative unit constituted by up to sixteen provinces. The Empire was separated into twelve (or later, fifteen) dioceses. Each diocese was governed by a praetor vicarius who was subjected to the praefectus .
Between the 4th and 6th centuries, Rome became more and more Christian. At the same time, the older administrative structure began to crumble. The senatorial aristocracy, especially in the provinces, remained a source of local authority. By this time, however, that authority was often vested in the spiritual office of bishop. It is therefore of little surprise that, as the Catholic and later the Eastern Orthodox churches began to define their administrative structure, they relied on the older Roman terminology to describe administrative units and hierarchy.
- Particular church
- Eparchy, a term in Eastern-Rite Catholicism, Eastern Orthodoxy, and Oriental Orthodoxy
- Ecclesiastical Latin
- Catholic Church in Great Britain
- List of the Roman Catholic dioceses of Ireland
- List of the Roman Catholic dioceses of the United States
- List of Church of England dioceses
- List of Church of Ireland dioceses
- Partenia, a cyber-diocese
- List of Bishops
- Dioceses of the Episcopal Church in the United States of America
- Virtually complete list of current and historical Catholic dioceses worldwide
- Another such list, in English and Norwegian
- List of current Anglican/Episcopalian dioceses