The Basilica of Saint Peter, officially known in Italian as the Basilica di San Pietro in Vaticano and colloquially called Saint Peter's Basilica, ranks second among the five major basilicas(The Latin word basilica (derived from Greek basiliké stoà, royal stoa), was originally used to describe a Roman public building, usually located at the centre of a Roman town. After the Roman Empire became officially Christian, the term came by extension to refer to a large, and important church that has been given special ceremonial rights by the Pope.) of Rome and its Vatican City enclave. Possibly the largest church in Christianity, it covers an area of 23,000 m² and has a capacity of over 60,000 people. One of the holiest sites of Christendom, it is believed to be the site of crucifixion and burial of the basilica namesake Saint Peter, one of the twelve apostles of Jesus and first Bishop of Antioch and later first Bishop of Rome. Tradition holds that his tomb is below the baldachino and altar; for this reason, many Popes, starting with the first ones, have been buried there. The current basilica was started in 1506 and was completed in 1626, and was built over the Constantinian basilica.

Contrary to popular belief, the basilica does not hold the distinction in the Roman Catholic Church of being the ecumenical motherchurch, as it is not the cathedral of the Pope (in fact, it is not a cathedral at all). That distinction belongs to the Basilica di San Giovanni in Laterano. However, due to the proximity of the Papal residence, most Papal ceremonies take place at St. Peter's. The basilica also holds a relic of the Cathedra Petri, the episcopal throne of the basilica's namesake when he led the Roman church, but which is no longer used. These are the sources of the confusion.