More than 100 Catholic cardinals will gather in the Sistine Chapel on the afternoon of March 12 to elect their new leader.
WHO CHOOSES THE POPE?
The new Pope will be chosen by a college of 120 Cardinals. Elected Cardinals who are over the age of 80 are excluded from the vote.
Pope Benedict XVI altered the rules before he abdicated – as have many of his predecessors – to ensure the new Pope would have to be elected with a two-thirds majority.
HOW IS A POPE ELECTED?
On the morning of March 12, the Cardinal electors will attend a mass before entering the Sistine Chapel in formal procession to begin the conclave at 4.30pm.
The Sistine Chapel is then swept for audio bugs and the cardinals-elect will not be allowed to tweet or talk with the outside world until a new Pope is chosen.
To vote, cardinals write their choice on a piece of paper, often under the Latin heading "Eligo in Summum Pontificem" ("I elect as Supreme Pontiff").
When casting his ballot, the cardinal slides the folded paper into a specially designed urn while invoking God as his witness in Latin.
At the end of the vote, counting can begin once the scrutineers have checked that the number of votes conforms to the number of electors.
There is no electronic voting machine or risk of e-fraud: as the votes are counted, a scrutineer calls out the name and a needle and thread is passed through each ballot. At the end of the count, the thread is knotted.
The electors vote four times a day until a two-thirds consensus emerges.
Historical methods intended to speed up the vote have been ditched, and the cardinals will not be forced to remain holed up each night in the ballot room.
They have been given an upgrade on the previous spartan lodgings given to electors within the Vatican, where they shared toilets and other facilities.
Now they enjoy hotel-like accommodation -- with individual bathrooms -- in a purpose-built residence, but even there security is tight: they have no radios, televisions, newspapers or any means of communicating with the world outside.
There will be no Internet either and smartphones are strictly off limits -- on pain of excommunication for breaking the secrecy of the conclave.
Should any of the cardinals be ill and unable to attend the vote, they can drop their ballot through a slit in a locked box brought to them in their rooms at the Vatican by selected "infirmarii" cardinals, trusted not to peek.
Once the vote is in, the ballot papers are burnt: black smoke curling from the Vatican's chimney means no decision has been made, white means a new pope has been elected.
The smoke was traditionally blackened by adding damp straw to the fire, but following confusion over several instances of grey smoke, the Vatican now adds a chemical to the fire to make sure the smoke emerges the correct colour.
And just in case even modern chemicals prove unreliable, the bells of St. Peter's Basilica will peal to tell the world "Habemus Papam" -- "We have a pope" before the chosen one emerges onto a balcony over St Peter's Square.
