The Papal Basilica of Saint Peter (Latin: Basilica Sancti Petri), officially known in Italian as Basilica Papale di San Pietro in Vaticano and commonly known as Saint Peter's Basilica, is a Late Renaissance church located within the Vatican City. Saint Peter's Basilica has the largest interior of any Christian church in the world. While it is neither the official mother church of the Roman Catholic Church nor the cathedral of the Pope as Bishop of Rome, Saint Peter's is regarded as one of the holiest Catholic sites. It has been described as "holding a unique position in the Christian world" and as "the greatest of all churches of Christendom".

In Roman Catholic tradition, the basilica is the burial site of its namesake Saint Peter, who was one of the twelve apostles of Jesus and, according to tradition, the first Bishop of Rome and therefore first in the line of the papal succession. Tradition and some historical evidence hold that Saint Peter's tomb is directly below the altar of the basilica. For this reason, many Popes have been interred at St. Peter's since the Early Christian period. There has been a church on this site since the 4th century. Construction of the present basilica, over the old Constantinian basilica, began on 18 April 1506 and was completed on 18 November 1626.