In Christianity, an episcopus vagans (plural episcopi vagantes; Latin for 'wandering bishops' or 'stray bishops') is a person consecrated, in a "clandestine or irregular way", as a bishop outside the structures and canon law of the established churches; a person regularly consecrated but later excommunicated, and not in communion with any generally recognized diocese; or a person who has in communion with them small groups that appear to exist solely for the bishop's sake.
David V. Barrett, in the Encyclopedia of New Religious Movements, specifies that now episcopi vagantes are "those independent bishops who collect several different lines of transmission of apostolic succession, and who will happily (and sometimes for a fee) consecrate anyone who requests it". Those described as wandering bishops often see the term as pejorative. The general term for "wandering" clerics, as were common in the Middle Ages, is clerici vagantes; the general term for those recognising no leader is acephali.
The Oxford Dictionary of the Christian Church mentions as the main lines of succession deriving from episcopi vagantes in the 20th century those founded by Arnold Mathew, Joseph René Vilatte and Leon Chechemian. Others that could be added are those derived from Aftimios Ofiesh, Carlos Duarte Costa, Paolo Miraglia-Gulotti, Emmanuel Milingo, Pierre Martin Ngô Đình Thục and Richard Williamson.
According to Buchanan, "the real rise of the problem" happened in the 19th century, in the "wake of the Anglo-Catholic movement", "through mischievous activities of a tiny number of independently acting bishops". They exist worldwide, he writes, "mostly without congregations", and "many in different stages of delusion and fantasy, not least in the Episcopal titles they confer on themselves"; "the distinguishing mark" to "specifically identif[y]" an episcopus vagans is "the lack of a true see or the lack of a real church life to oversee".