The arcane process of choosing a successor to Pope Benedict XVI will quickly follow his official departure from office on Feb 28, and the world will soon find itself focusing on the chimney of the -Sistine Chapel.
The College of Cardinals, which currently has 117 members, will convene within the walls of the Vatican Chapel for a centuries-old ritual known as a conclave.
They will be alone except for servants, emergency medical staff and, on one previous occasion, an Italian journalist disguised as a servant attempting to leak news to the world.
The cardinals eat, vote and sleep within sealed areas until they have selected a new pope. No contact is allowed with the outside world. The threat of excommunication hangs over anyone tempted to break the vow of silence.
Unusually, there will be no representative of England and Wales this time. Vincent Nichols, who became Archbishop of Westminster in 2009, has not been made a cardinal.
Any baptised Roman Catholic male is eligible for election, but since 1378 only cardinals have been selected.
The process can take days. A handful of candidates will preach at Mass to the college. A lengthy debate is likely in choosing Pope Benedict's successor, given the surprise of his resignation.
Two ballots are held each morning and two each afternoon for up to three days until a two-thirds majority is reached.
The cardinals write their choice on a ballot paper and place it in an urn. The votes are added up by scrutineers, and, if there are no irregularities, the result is recorded and the ballot papers burned.
If the colour of the smoke billowing from the chapel's stovepipe is white, then a new pope has been chosen. If it is dark, then there has to be another vote. Previously, damp straw was used to darken the smoke. Since 1963, a liquid dye has been used.
The conclave has been the procedure for choosing the pope since 1417, and is the oldest ongoing method for choosing the leader of any major institution. There has been no significant challenge to a decision by the conclave.