The conclave that begins in Vatican City on Wednesday is the process of electing the next leader of the world's 1.4 billion Catholics. Shrouded in mystery, with all those involved sworn to secrecy on threat of ex-communication, what do we know about what goes on behind the sealed doors of the Sistine Chapel?
At stake with the election of a new pope is the direction of the Catholic Church, a 2,000-year-old institution with huge global influence but which is battling to adapt to the modern world, and to recover its reputation after the scandal of child sexual abuse by priests.
The process of this election – the conclave – however, is one element not in line for modernisation. Shrouded in secrecy, its name is derived from the Latin cum (with) and clavis (key) – meaning a "room that can be locked".
This secrecy has seen the conclave enshrined in the popular imagination. The film Conclave, based on the bestselling novel by British author Robert Harris, picked up an Oscar, four BAFTAs and a Golden Globe during this year's awards season.
'Princes of the Church'
The 133 cardinals – the so-called "Princes of the Church" – who will vote will gather on Wednesday afternoon under the frescoed splendour of the Sistine Chapel at the Vatican.
A cardinal (from the Latin cardinalis or principal) is a high dignitary of the Catholic Church chosen by the pope to assist him in his government. They form the top echelon of the Catholic Church, with their scarlet robes representing the blood of Christ.
The creation of cardinals reflects the political views of the pontiff, who normally uses this power to shape the selection of his own successor. The current College of Cardinals is a diverse group, thanks to Pope Francis appointing figures from far-flung diocese, some gaining a cardinal for the first time – such as Brunei, Mongolia and South Sudan.
This diversity means some observers are predicting a protracted process. Vatican affairs specialist Marco Politi told French news agency AFP that, given the unknowns, this conclave could be "the most spectacular in 50 years".
Oath of secrecy
During the conclave, the cardinals are forbidden from contacting the outside world. They will stay at the Santa Marta guesthouse – although prior to 1996 they slept on camp beds in the Apostolic Palace, which is connected to the Sistine Chapel.
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All windows in the conclave zone are darkened to guarantee privacy. Ahead of the vote, technicians deactivate all technological devices installed in recent years in the Sistine Chapel and sweep for secret recording devices.
The day before the conclave they will install "approximately 80 lead seals at all entrances to the perimeter".
The extreme secrecy required extends to these technicians too, and all support staff – cleaners, cooks, doctors and nurses, drivers and elevator operators. All took an oath of secrecy on Monday. The punishment for breaking it? Automatic ex-communication.
Twelve technicians and maintenance craftspeople will remain inside the Sistine Chapel for the duration of the conclave, maintaining temperature, lighting and electrical systems, and assisting with ceremonial logistics such as operating the famous stove – which is now activated by remote control.
The vote
On Wednesday, the day the conclave begins, the cardinal electors take part in a morning mass in St Peter's Basilica. They will then gather in the Pauline Chapel of the Apostolic Palace at 4:15pm and invoke the assistance of the Holy Spirit in making their choice.
They proceed at 4:30pm to the Sistine Chapel, where the election will be held, and take an oath vowing secrecy and promising that, if elected, they will conduct the role faithfully.
The master of ceremonies gives the order extra omnes ("everybody out") and all those not permitted to vote leave the chapel.
The masters of ceremonies then distribute ballots to the electors. Lots are drawn to select three to serve as "scrutineers", three infirmarii to collect the votes of cardinals who fall ill and three "revisers" who check the ballot counting by the scrutineers.
Cardinals are given rectangular ballots inscribed with the words Eligo in Summum Pontificem ("I elect as supreme pontiff"), with a blank space underneath. They write down the name of their choice for future pope, preferably in handwriting which cannot be identified, and fold the ballot paper twice.
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Each cardinal takes turns to walk to the altar, carrying his vote in the air so that it can be clearly seen, and says aloud the following oath: "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."
The electors place their folded paper on a plate, which is used to tip the ballots into a silver urn on the altar, in front of scrutineers. They then bow and return to their seats.
Once all ballots are collected, scrutineers shake the urn to mix the votes up, transfer them into a second container to check there are the same number of ballots as electors and begin counting them.
Two scrutineers note down the names while a third reads them aloud, piercing the ballots with a needle through the word Eligo and stringing them together. The revisers then double-check that the scrutineers have not made any mistakes.
If no one has secured two-thirds of the votes, there is no winner and the electors move straight on to a second round. There are two pairs of votes per day, morning and afternoon, until a new pope has been elected.
The ballots and any handwritten notes made by the cardinals are then destroyed, burnt in a stove in the chapel. It emits black smoke if no pope has been elected and white smoke if there is a new pontiff.
The smoke is turned black or white through the addition of chemicals – potassium perchlorate, anthracene (a component of coal tar) and sulfur to produce black smoke, or potassium chlorate, lactose and chloroform resin to produce the white smoke.
If voting continues for three days without a winner, there is a day of prayer, reflection and dialogue. If after another seven ballots there is no winner, there is another day of pause.
If the cardinals reach a fourth pause with no result, they can agree to vote only on the two most popular candidates, with the winner requiring a clear majority.
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In 2013, the conclave lasted 27 hours, and in 2005 it was 26 hours. The shortest on record took place in 1503, when it took cardinals just 10 hours to elect Pope Pius III.
As for the longest, in the 13th century it took almost three years, beginning n 1268 – 1,006 days to be exact – to choose Pope Clement IV's successor.
From late 1269 the cardinals allowed themselves to be locked in to try to reach a decision.
When they still hadn't managed this by June 1270, frustrated locals tore the roof off in a bid to speed things along – inspired by a quip by an English cardinal that without the roof, the Holy Spirit could descend unhindered.
When a cardinal is elected pope, the masters of ceremonies and other non-electors are brought back into the Sistine Chapel and the cardinal dean asks the winner: "Do you accept your canonical election as Supreme Pontiff?"
As soon as he gives his consent, he becomes pope – and is free to celebrate, as John Paul II did in 1978, reportedly walking around pouring Champagne for the cardinals and singing Polish folk songs.
Controversies
Conclaves have seen their share of controversy over the centuries. This year, United States President Donald Trump last week posted an AI-generated image of himself dressed as the pope on his Truth Social platform, after joking that he would be his own first choice for the next pontiff, drawing the ire of the Church.
The New York State Catholic Conference wrote in a post on X: "There is nothing clever or funny about this image, Mr President. We just buried our beloved Pope Francis and the cardinals are about to enter a solemn conclave to elect a new successor of St Peter. Do not mock us."
Last week, France's President Emmanuel Macron was accused by Italian media of attempted interference in the conclave, after he held a series of meetings with cardinals and Church officials while in Rome for Pope Francis's funeral.
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In 2013, so convinced were they of his success, upon sight of the famous white smoke signal the Italian bishops' conference sent out a press release congratulating Italian Cardinal Angelo Scola – when Pope Francis had just been elected.
In the days leading up to the conclave, Italian newspapers openly promoted Scola as the next pope, appearing to have missed the warning contained in a traditional Italian saying that front-runners at a papal conclave are often disappointed: "He who enters a conclave as a pope, leaves it as a cardinal."
In 1241, when the conclave was dragging on, the head of Rome's government locked the cardinals into a dilapidated building and refused to clean the lavatories or provide doctors for those who fell ill.
According to Frederic Baumgartner in his Behind Locked Doors: A History of the Papal Elections, the cardinals only reached a decision – electing Celestine IV – after one of them died and the Romans threatened to exhume his corpse and have it make decisions.
(with newswires)
