There will be a mass at St.. Peter's Basilica tomorrow, and then the voting process begins for a new pope.
The 115 cardinals who will elect a new pope held their final meeting before voting begins.
During the conclave in the Sistine Chapel, the cardinals will pray and vote in silence.
The first cardinal to receive at least 77 votes will be the next pope.
The so-called 'smoke watch' begins Tuesday night.
After dark, lights will shine on a chimney on top of the Sistine Chapel.
Black smoke means the voting continues. White smoke and church bells means a new pope has been chosen.
The conclave is expected to last two or three days.