Roman Catholic Cardinals begin a conclave today to elect the Church's 266th pontiff and a successor to Pope Benedict, who abdicated unexpectedly last month.
One of the world's oldest and most secret electoral processes will be attended by 115 cardinals who were under 80 years old when Benedict abdicated. Two other eligible cardinals are not attending - one for health reasons, one because of his involvement in a sex scandal. Ninety cardinals aged 80 or over cannot take part. The person chosen as pope does not have to be one of the cardinal electors, but in practice now always is.
The elector cardinals come from 48 countries. Italians make up the biggest single national bloc, with 28 cardinals against 11 from the United States, six from Germany and five each from India and Brazil. Sixty cardinals come from Europe, 19 from Latin America, 14 from North America, 11 from Africa, 10 from Asia and one from Oceania.
The cardinals will sleep in Vatican hotel Casa Santa Marta behind St Peter's Basilica. They will be banned from communicating with the outside world - no phones, television or Internet.
They will start their meeting at 4:30 p.m. in the Sistine Chapel, under Michelangelo's frescoes of the Last Judgement and of Bible scenes including the creation panel with the finger of God and the finger of Adam nearly touching.
The cardinals will cast their first vote this afternoon. From tomorrow they will vote twice each morning and twice each afternoon. The cardinals will suspend voting on Saturday if they have not chosen a pontiff. To win, a candidate needs a two-thirds majority, or at least 77 votes.
The word conclave (from Latin "cum clave", or "with a key") dates back to the protracted election of Celestine IV in 1241, when cardinals were locked up in a crumbling palace. One conclave in the 13th century lasted two years, nine months and two days. The average length of the last nine conclaves of the 20th century was about three days. The last conclave, which elected Benedict in 2005, lasted barely 24 hours.
After cardinals cast their votes on papers printed with the Latin words "Eligo in Summum Pontificem" ("I choose as Supreme Pontiff"), the ballots are burned and smoke pours from a makeshift chimney above the Sistine Chapel.
The smoke signals, telling the world whether or not cardinals have elected a new pope, are expected at around noon and 7 p.m. each voting day. However, smoke could emerge earlier if the new pontiff is elected in the first ballot of one of the sessions.
Black smoke marks an inconclusive vote; white smoke and the tolling of the bells of St. Peter's Basilica mean a pope has been elected.
When a pope is chosen, a senior cardinal appears on the balcony of St. Peter's Basilica and announces in Latin: "Annuntio vobis gaudium magnum. Habemus Papam" ("I announce to you great joy. We have a pope"). He identifies the new pope by his given name, with his first name translated into its Latin version, and then announces the papal name the new leader of the Church has chosen.
The papal names most often chosen have been John (23 times), Gregory (16), Benedict (16), Clement (14), Innocent (13), Leo (13) and Pius (12).
After the announcement, the new pope steps forward to deliver his first public address and his first "Urbi et Orbi" ("To the City and the World") blessing in front of the crowds gathered in St. Peter's Square.