Episcopi vagantes (Latin for "wandering bishops") are persons who have been ordained as bishops in a Christian church in some irregular fashion, especially those claiming to have valid Catholic orders although their ordinations were not authorized by the Roman Catholic Church. The Roman Catholic Church considers some such ordinations valid but illegal. On the other hand, Eastern Orthodoxy considers them to simply not be ordinations.
Many of these claim succession from the see of Utrecht, or from Eastern Orthodox or Eastern-Rite Catholic churches; others from Roman Catholic bishops that have ordained their own bishops after disputes with the Vatican.
According to Roman Catholicism, the ordination of a bishop is valid, even if illegal, if the bishop is in a line of succession of bishops dating back to the Apostles and the rites of ordination are properly performed (see Apostolic succession). That is why Catholics recognize the validity of ordinations in Eastern Orthodox and some other churches, but do not recognize Protestant ordinations.
Many people have claimed ordinations as bishops where it is questionable whether the ordination ever took place.