In the wake of Vatican II, several arch-conservative Roman Catholic groups began to adopt a critical attitude towards the hierarchy. The largest of these groups later became the Society (or Fraternity) of Saint Pius X under the leadership of French Archbishop Marcel Lefebvre (1905-1991). Lefebvre, however, never questioned the legitimacy of Pope Paul VI (1897-1978), or that of his successors. Lefebvre’s view was that they were leaders of dubious doctrines and actions (thus justifying Lefebvre in promoting what, according to Rome, amounted to a schism), but did not conclude that such wrongdoings should automatically invalid their Papal canonical role. Inside and outside the Society of Saint Pius X, more radical groups emerged, each concluding that, after Vatican II, the Popes had lost their legitimacy as a result of their heretical teachings; this implied that the Holy See of Rome (“Sedes”, in Latin) was technically “vacant”, i.e. there was no legitimate Pope. Hence the name of “Sedevacantism” given to the movement, which was vehemently critical of Lefebvre and his Society of Saint Pius X. The latter, in fact, although critical of the Pope, continued to pray for him in its Masses with the ritual formula “una cum Pontifice nostro” (“in unity with our Pope”). Sedevacantists regarded what they called the “una cum Masses” as ipso facto invalid, just as both Sedevacantists and members of the Lefebvre movement regarded Masses celebrated according to post-Vatican II liturgical renewal as invalid.

Sedevacantism was never a well-organized movement, consisting as it did of several small groups, often divided on questions of leadership and on the finer points of how “non-una cum” Masses should be celebrated. The very fact that they considered the Holy See to be vacant, meant that Sedevacantists by definition could not recognize an international authority, and it kept their movement divided. Some influential centers did emerge, however. Many Sedevacantist leaders were consecrated as Bishops in the late 1970s and early 1980s by arch-conservative Vietnamese Archbishop Pierre-Martin Ngô-Dhinh Thuc (1897-1984). These consecrations, not authorized by the Vatican, were, according to Roman Catholic Canon Law, illicit but not invalid (and they led ultimately to Thuc’s excommunication). This means that Thuc’s consecration of the Sedevacantist leaders as Bishops was regarded as valid, although they were automatically excommunicated. They were, however, according to Roman Catholic Canon Law, “real” Bishops, with the power to consecrate other Bishops in turn and to validly ordain priests (forthwith excommunicated by virtue of the fact of their ordination by an excommunicated Bishop). The question is quite important in Catholic Canon Law and doctrine, which states that a validly ordained priest (although excommunicated), when pronouncing the words of the consecration in the Mass, really does convert the bread and wine into the body and blood of Jesus Christ (something an invalidly ordained priest is not empowered to do). Thus, thanks mostly to Archbishop Thuc (who died in 1984 fully reconciled with Rome) and to more than one hundred “Thuc Bishops” ordained directly or indirectly by him, Sedevacantists could rightly claim to have “real” priests and to be able to offer “real” Masses to their followers.

There may be some ten thousand Sedevacantists throughout the world, with the most important centers in the U.S., Mexico, France, Italy, Germany and the Czech Republic. Most of them believe that forming a central organization would be tantamount to establishing a schismatic alternative Roman Catholic Church. They prefer to remain a network of small groups, and see themselves as the only surviving remnant of the one true post-Vatican II Catholic Church. One of their main problems is how to respond to the issue of the future of Catholic authority. By definition, they regard the Pope as essential for the Church’s very survival and infallibility, but, at the same time, they maintain there was no (legitimate) Pope in Rome during the John Paul II era. A large majority of Sedevacantists dismiss as non-canonical, and even ridiculous, the very idea that they could convene a conclave and elect a Pope of their own; they prefer to wait for a solution to come directly, and perhaps unpredictably, from God, whose ways, they say, are after all not human ways. A few Sedevacantists, on the other hand, are “conclavist”, i.e. they believe a conclave should be called (composed of all, or at least most, Sedevacantist Bishops), and a new Pope duly elected. Conclavists realize nonetheless that, should a conclave be organized, the majority of the Sedevacantist Bishops would refuse to attend it, and some groups regard a conclave as certainly desirable but, at least for the time being, impracticable. Attempts have been made to organize a conclave, however: in 1994, for example, some twenty Sedevacantist Bishops from twelve different countries met in Assisi, Italy, and elected as Pope a South African priest (and former student at Lefebvre’s seminary), Victor Von Pentz, under the name of Linus II. He currently resides in the U.K. and maintains but a limited following.

Some conclavists have, on the other hand, joined other alternative Popes (“Antipopes”, according to Roman Catholic theology), who, even before the full development of the Sedevacantist network, had claimed that their role was based both on the alleged heresies of Vatican II and on mystical visions calling them to the Pontificate without the need of any conclave or election. One of the earliest “pretenders” was a French priest, Michel-Auguste-Marie Collin (1905-1974), who claimed to have been called by Heaven itself to become “Pope Clemens XV” during Vatican II, in 1963. Collin established an alternative “Vatican” in Clémery, Lorraine, where he also founded a Renewed Church of Christ, known outside France as the Church of the Magnificat. After Collin’s death in 1974, his Church nearly collapsed entirely, and is now reduced to a small remnant of what it once was. One of Collin’s followers, however, the Québec priest Gaston Tremblay (b. 1928), had already ceased to recognize the French claimant in 1968, and had proclaimed himself “Pope Gregory XVII”. His movement, the Apostles of Infinite Love, is the largest of its kind in North America.

Tremblay’s main competitor was Clemente Domínguez y Gómez (1946-2005), one of the seers in the alleged Marian apparitions of Palmar de Troya, Spain (1968-1976) and later a “Thuc Bishop”, consecrated by the Vietnamese Archbishop on January 11, 1976. In 1978, Domínguez (in the meantime blinded by a car accident in May 1976) revealed that he had been mystically designated by Jesus Christ as the new Pope in a 1976 vision, and his followers confirmed his election as “Pope Gregory XVII” (the same name adopted by Tremblay in Québec). His “Catholic, Apostolic and Palmarian Church” (named after the town of Palmar de Troya) is probably the single largest organization bowing to the authority of an “alternative” Pope, with more than a thousand followers in Spain and several hundreds more internationally. In the 1990s, however, Domínguez was accused of sexual immorality with several nuns of the order he had established in the meantime; in 1997, he admitted his sins and asked for his community’s forgiveness. Most followers remained loyal to Domínguez and to his hand-picked successor, former lawyer and “Thuc Bishop” Manuel Alonso Corral. Others, however, have both doubted the sincerity of Domínguez in his apology and questioned his decision to appoint a successor rather than leave this choice to a conclave including the many cardinals he had in the meantime appointed from among his Bishops. At the end of 2000, 17 Bishops with a couple of hundred followers left the Palmarian Church, and formed a splinter movement known as “The Tribe”.  Dominguez died on March 21, 2005. It has been succeeded by Manuel Alonso Corral, who has been crowned as Pope on March 26 under the name of Peter II.

Other claimants to the role of Pope also exist throughout the world.