The document that determines what happens when the Apostolic See becomes vacant and a new pope is to be elected is the Apostolic Constitution Universi Dominici Gregis, issued by Pope John Paul II on 22 February 1996.
By the way, the word conclave, meaning literally “with key”, refers to the gathering of the Cardinal electors in the Vatican to elect a new pope, where they are so to speak “locked away.”
Which cardinals may vote for a new pope? The constitution determines that only those beneath the age of 80 when the See becomes vacant may vote, and there should be no more than 120 of these. The voting itself is done in the Sistine Chapel, which is presided over by Michelangelo’s well-known fresco of the Last Judgment. It is a sombre reminder that the cardinals will one day be held to account for all their actions, in this case for their choice of a shepherd for the universal church.
Whereas in earlier conclaves the cardinals resided in the area of the Sistine Chapel itself throughout the days of the conclave, they now live in the more comfortable Domus Sanctae Marthae, or House of St Martha, built in 1996 on the edge of Vatican City.
All other guests must leave during the conclave so that the cardinal electors have complete privacy. Even the shutters on the windows are locked for this purpose and the cardinals have no contact with the outside world. The cardinals are taken back and forth to the Sistine Chapel by bus during the conclave, although some cardinals in the last conclave preferred to walk, scrutinised by Vatican security staff.
Like the cardinals themselves, the cooking and cleaning staff and the others who assist the cardinals take an oath of silence, promising “absolute and perpetual secrecy” regarding anything related to the election. They also “promise and swear to refrain from using any audio or video equipment capable of recording anything which takes place during the period of the election within Vatican City” (n. 48).
On the morning the conclave begins, the cardinal electors take part in a solemn Mass for the election of the pope in St Peter’s Basilica. That afternoon they chant the Veni Creator, a hymn to the Holy Spirit, in the Pauline Chapel of the Apostolic Palace and then process to the Sistine Chapel, which has been checked beforehand to ensure that no audiovisual equipment has been secretly installed to record or transmit the proceedings.
There they take the oath to observe all the prescriptions of the Apostolic Constitution Universi dominici Gregis, including that of perpetual secrecy regarding the election, and they attend a meditation preached by an ecclesiastic.
That afternoon, one ballot may be held. On the following days there are two ballots in the morning and two in the afternoon until someone is elected by a two-thirds majority. Before depositing their written ballots in the box placed on the altar each cardinal says aloud, “I call as my witness Christ the Lord who will be my judge, that my vote is given to the one who before God I think should be elected” (n. 66). After the ballots have been counted and recorded they are burned.
If after three days no one has been elected, there is a pause for prayer and informal discussion for no more than one day, and then the voting resumes for another seven ballots, when there is another pause, and so on successively until someone is elected (cf. n. 75).
If no one is elected after four such series of ballots, in subsequent ballots the Cardinals vote on only the two names who received the largest number of votes in the previous ballot until one of them has a two thirds majority, as Pope Benedict XVI determined in a Motu proprio in 2007. At this point they send white smoke up the chimney to announce to the world that a new pope has been elected.
The newly elected pope is then asked whether he accepts the election and by what name he wishes to be called. The other cardinals come up and make an act of homage and obedience to him, and together they make an act of thanksgiving. After this the new pope goes to the balcony of St Peter’s Basilica, where the senior cardinal deacon announces to the people that the election has taken place and he proclaims the name of the new pope, who gives the apostolic blessing.
Until then, “the universal church, spiritually united with Mary, the Mother of Jesus, should persevere with one heart in prayer” (n. 84) for the cardinals who are to elect the pope and for the new pope himself.