The term is Latin, and means "wandering bishops" (or "stray bishops"). Those to whom it is applied see it as pejorative.
In modern times, the main streams of succession deriving from episcopi vagantes are those founded by Arnold Mathew, Joseph René Vilatte, Leon Chechemian, and, since the 1970s, Pierre Martin Ngô Đình Thục
Some theologians, within the Roman Catholic Church and elsewhere, question whether all such consecrations have effect, on the grounds that an ordination is for service within a specific Christian Church. Therefore an ordination ceremony that concerns only the individual himself does not, they say, correspond to the definition of an ordination and is without effect. The Holy See has not commented on the correctness or erroneousness of this theory. Other theologians, notably those of the Eastern Orthodox Church, dispute this notion, but it can be seen how such an understanding opens up the possibility of valid but irregular consecrations proliferating outside the structures of the "official" denominations.
A distinction is also made in Catholic theology between the conferral of the sacramental powers associated with the episcopacy and the conferral of jurisdiction: the power of a bishop to govern his people. In Roman Catholic canon law, a bishops's sacramental power is to some extent entwined with his jurisdiction (or lack of it): jurisdiction is required for valid celebration of the sacraments of Penance and Matrimony. Jurisdiction can be conferred only within the official structures of the Church under the Pope. Catholic episcopi vagantes sometimes appeal to the principle that, in emergency situations, jurisdiction is automatically "supplied" even where it has not explicitly been conferred ("Ecclesia supplet").
The Eastern Orthodox Church's position has been summarised as follows:
This applies to the validity and efficacy of the ordination of bishops and the other sacraments, not only of the Independent Catholic Churches, but also of all other Christian Churches, including the Roman Catholic Church, Oriental Orthodoxy, and the Assyrian Church of the East.
Anglican ordinations are not recognised as valid by the Roman Catholic Church. In recent times, some have claimed to discern intimations from the Roman Catholic Church that the non-recognition of Anglican ordinations might be re-examined. The ordination of women in the Anglican Communion has complicated this issue.
Many, if not most, episcopi vagantes are associated with Independent Catholic Churches, and in some cases the bishop is almost the only clergyman of the group. They may be very liberal or very conservative. Episcopi vagantes may also include several conservative "Continuing Anglicans" who have broken with the Anglican Communion over various issues such as Prayer Book revision, ordination of women and the ordination of unmarried, non-celibate individuals (including homosexuals).
A similar declaration was issued with regard to Archbishop Emmanuel Milingo's conferring of episcopal ordination on four men - all of whom, by virtue of previous Independent Catholic consecrations, claimed already to be bishops - on 24 September 2006: the Holy See, as well as stating that, in accordance with Canon 1382 of the Code of Canon Law, all five men involved incurred automatic ("latae sententiae") excommunication through their actions, declared that "the Church does not recognise and does not intend in the future to recognise these ordinations or any ordinations derived from them, and she holds that the canonical state of the four alleged bishops is the same as it was prior to the ordination."
In contrast, the Holy See has questioned neither the validity nor the canonical effect of the consecrations that the late Archbishop Marcel Lefebvre performed in 1988 for the service of the relatively numerous followers of the Traditionalist Catholic Society of St. Pius X that he had founded.
Some have questioned the mental capacity of Archbishop Ngô to form the requisite intention to consecrate. On this question it would be extremely difficult to obtain a definitive objective judgement. Ngô was advanced in age and was reportedly experiencing a dementia at the time of his actions in question.