An apostolic vicariate is a form of territorial jurisdiction of the Roman Catholic Church established in missionary regions and countries where a diocese has not yet been established. It is essentially provisional, though it may last for a century or more. The hope is that the region will generate sufficient numbers of Catholics for the Church to create a diocese.
An apostolic vicariate is led by a vicar apostolic who is usually a titular bishop. While such a territory can be classed as a particular church, according to canon 371.1 of the Latin Code of Canon Law, a vicar apostolic’s jurisdiction is an exercise of the jurisdiction of the Pope — the territory thus comes directly under the pope as “universal bishop”, and the pope exercises this authority through a “vicar”. This is unlike the jurisdiction of a diocesan bishop, whose jurisdiction derives directly from his office.
Like any ecclesiastical jurisdiction, an apostolic vicariate may be administered by the bishop of a neighbouring diocese, or by a priest appointed transitionally as an apostolic administrator. As in a regular diocese, the vicar apostolic may appoint priests as vicars exercising limited jurisdiction over the apostolic vicariate. Normally, however, an apostolic vicariate is administered by a titular bishop of its own.
An apostolic vicariate is to be distinguished from an apostolic prefecture, a similar type of territory whose chief distinction from an apostolic vicariate is that its prefect is not a bishop, but a mere priest. The latter is not organised enough to be elevated to apostolic vicariate. The less developed instance is the mission sui iuris, which other than the ones mentioned before is not a particular Church, although it shares some similarities to one; for it as well, a superior is named. The usual sequence of development is mission, apostolic prefecture, apostolic vicariate, and finally diocese.
The apostolic vicariate is distinguished from a territorial abbacy (or “abbey nullius”) — an area not a diocese but under the direction of the abbot of a monastery.