The Society of Saint Pius X (SSPX; Latin: Fraternitas Sacerdotalis Sancti Pii X, lit. 'Priestly Fraternity of Saint Pius X', FSSPX) is a traditionalist Catholic organization founded in 1970 by Archbishop Marcel Lefebvre. Considered schismatic by the Catholic Church, the society comprises priests and seminarians and is associated with a worldwide network of chapels, schools, religious communities, and lay supporters. It is known for its opposition to several reforms associated with the Second Vatican Council. Members are commonly called Lefebvrists, Lefebvrians, or Lefebvrites, terms SSPX rejects. Following decades of canonical disputes, the Holy See formally declared the society to be in schism and its adherents excommunicated in July 2026 following illicit consecrations of bishops. Named after Pope Pius X for his anti-modernist stance, the society retains the Tridentine Mass and pre-Vatican II liturgical books in Latin. France serves as the home of the largest demographic of FSSPX members, with the United States in second place. It has more than 700 priests among 1,482 total members. Estimates of the number of laypeople who attend SSPX Masses vary significantly; the society cites a figure of 600,000, while media estimates have suggested an active following of 150,000 to 200,000. Groups derived from SSPX include the Priestly Fraternity of Saint Peter (FSSP), authorized by Pope John Paul II in 1988, and the sedevacantist Society of Saint Pius V (SSPV). Initial tensions with the Holy See came to a head in 1988, when Lefebvre consecrated four priests as bishops in Écône, without an apostolic mandate and against a personal warning from Pope John Paul II incurring automatic (latae sententiae) excommunication. The society was declared schismatic. Attempts to mend the rift began in the 2000s, when the excommunications incurred for the 1988 consecrations were remitted in 2009 at the bishops' request, and ecclesiastical jurisdiction was extended to SSPX-administered confessions and marriages by Pope Francis in 2017. However, when SSPX consecrated a new generation of bishops in a similar manner in 2026, its bishops incurred excommunication anew, the society was declared schismatic a second time, and the faculties that had been granted by Pope Francis were rescinded. On both occasions, SSPX disputed that any penalty had been incurred, citing a moral and theological crisis in the church.