There is no clear frontrunner in the race to replace Pope Benedict XVI, the first pope to resign in over 700 years.
At 9am GMT, prayers will begin with a special mass in St Peter's Basilica.
This is followed at 3:30pm GMT with a procession into the Sistine Chapel, where the cardinals will take an oath of secrecy.
That is followed by a meditation delivered by elderly Maltese Cardinal Prosper Grech and then the master of papal liturgical ceremonies gives the order ""Everyone out" – at which point all but those taking part in the conclave leave chapel.
The cardinals vote just once on the first day of the conclave and results from that initial vote are expected around 7pm GMT on Tuesday.
The Vatican has already said it expects the smoke from the burning of the ballots to be black, indicating no clear winner or new pope.
For a winner to be declared he must receive two-thirds of the vote — 77 votes in total.
Ballots on subsequent days will be burnt at around 11am GMT after two rounds of voting in the morning and at around 6pm GMT after two rounds in the afternoon. The smoke is famously turned white if there is a new pope.
Three frontrunners have emerged - Italy's Angelo Scola, Brazil's Odilo Scherer and Canada's Marc Ouellet.
There has been widespread speculation that the Vatican may elect an African Pope, with Cardinal Peter Turkson being labelled the continent's best hope by the global media.
Image: © Getty
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