Conclave to elect a new pope: Interactive video
Step inside our "virtual Sistine Chapel" as the BBC's Philippa Thomas explains what happens in the conclave, the centuries-old process of electing a new pope which begins on Tuesday.Continue reading the main story
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When the cardinals enter the Sistine Chapel they take an oath of secrecy, then the Latin command "extra omnes!" (everyone out!) instructs all those not involved in the election to leave before the doors are shut and locked. Once inside, the cardinals are cut off from contact with the outside world: radios, newspapers and mobile phones are banned.
When not voting in the chapel, they live, eat and sleep in the nearby St Martha's House, where telephones and TVs are disconnected. A few carefully vetted staff are allowed to attend to the cardinals. A cardinal may leave in case of medical emergency but other than that, no-one can leave until a new pope is elected.
Each cardinal writes the name of his choice on a ballot paper, printed with the words "Eligio in Summum Pontificem" (I elect as Supreme Pontiff). He approaches the altar where he prays before placing his ballot on a plate and tipping it into an urn. A smaller urn is used to collect the ballots of any cardinals in the conclave who are too ill to attend the chapel.
After all the votes have been cast, three scrutineers mix, count and open them, reading out the names and joining the papers together on a thread. The papers are then burned in a stove at the back of the chapel. If no decision has been reached, chemicals are added to create black smoke but if one cardinal has gained a two-thirds majority then white smoke is given off, signalling that a new Pope has been chosen.
Of the 115 cardinals in the conclave, 60 come from Europe - 28 from Italy alone. Some 19 are from Latin America and 14 are from North America, with Africa and Asia roughly equal at 11 and 10 apiece. Just one cardinal is attending from Oceania: the Australian George Pell.
But the make-up of the conclave is at odds with the distribution of Catholics in the world where Latin America accounts for by far the biggest population at 41% of the global total. Europe has 24% followed by Africa at 15%. And these proportions are shifting: Catholicism has grown in Africa and Asia in the past 40 years while declining in Europe.
Popes tend to have pastoral experience and knowledge of the Curia, the Church's administrative body.
The Archbishop of Milan Angelo Scola, 71, is the most prominent Italian candidate. A conservative, he was close to Popes John Paul II and Benedict.
Canadian Marc Ouellet, 68, has headed the Congregation for Bishops since 2010; and Ghana's Peter Turkson, 64, is the relator, or general secretary, of the Synod for Africa.
Other contenders include Leonardo Sandri of Argentina, Christoph Schoenborn of Austria, and Timothy Dolan of the United States.
Produced by Christine Jeavans, Steven Atherton, Mark Bryson, Miho Tanaka and Jonathan Spencer