Leaders of the Roman Catholic Church are meeting for the final time before the process of electing the new Pope begins on Tuesday.
Following the resignation of Pope Benedict XVI, 115 cardinals - the Catholic Church's most senior priests - have travelled to the Vatican to make the decision.
The Vatican in Rome is the home of the Catholic Church.
What will happen?
The election process - or Conclave - begins on Tuesday morning.
The cardinals meet in a secluded hotel in the Vatican, before celebrating Mass in St Peter's Basilica.
After lunch, they will go into the Sistine Chapel - which is inside the Pope's official residence - and one vote will be held that evening.
A cardinal needs to get at least two thirds of the votes to become Pope.
The ballot papers used will be burnt after the vote, and the smoke will drift out of the chapel's chimney.
White smoke means a new Pope has been chosen.
If the smoke is black, it means the cardinals are still making up their minds, and from Wednesday two votes will be held each morning and afternoon until a decision is made.
If no result is reached by Friday, the cardinals will take Saturday off for a day of prayer and reflection.
Special technology is being used to jam any mobile phones or other devices which could breach the strict secrecy of the election process.
Red curtains have been hung on the balcony of St. Peter's Basilica, from where the new Pope will be introduced to the crowds once he is elected.