Institution
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 comes directly under the pope as "universal bishop", and the pope exercises this authority through a "vicar".[1]
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, a titular bishop is appointed to administer the apostolic vicariate. When someone who does not qualify or has not been ordained as bishop is appointed ad interim, he may be styled Pro-vicar.[2]
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 titular bishop, but a priest. The prefecture is not considered 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; at its head, an ecclesiastical superior is named. The usual sequence of development is mission, apostolic prefecture, apostolic vicariate, and finally diocese (or even archdiocese). See also apostolic exarch for an Eastern Catholic counterpart.
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.
Starting in 2019, new vicars apostolic, although they are (or become) bishops, are no longer assigned titular sees.