Cardinals have moved into the Vatican to begin voting on the new Pope, but there is no clear frontrunner to take over as head of the Roman Catholic Church.
The 115 cardinal electors will live inside the Vatican walls completely cut off from the outside world until they have made their choice.
Jamming devices have been installed to prevent bugging or communication in or out.
The prayers began with a special mass in St Peter's Basilica .
The Vatican said in advance of the first round of voting that it expected the smoke from the burning of the ballots to be black, indicating no papal selection has taken place.
They will vote four times daily until two-thirds can agree on a candidate.
The election was prompted by the surprise abdication of Benedict XVI.
The 85-year-old stepped down last month saying he was no longer strong enough to lead the church, which is beset by problems ranging from a worldwide scandal over sexual abuse to allegations of intrigue and corruption at the Vatican bank.
Benedict's resignation and the recent damage to the Church's reputation make the choice of the cardinal-electors especially hard to predict.
Candidates named as contenders include Cardinal Angelo Scola of Milan, Brazil's Odilo Scherer, and the US Cardinal Timothy Dolan - though he told one interviewer anyone who thought he was in with a chance might be "smoking marijuana".
From Wednesday, two votes will be held each morning and afternoon - with ballots burned after each session - until one candidate attains a two-thirds majority (77 votes).
Then the smoke will be white, meaning the 266th bishop of Rome will have been chosen.