The conclave will end when a cardinal receives 77 out of a possible 115 votes. When the 266th pope has been chosen and the world's 1.2 billion Catholics have a new leader, puffs of white smoke will emerge from the Sistine Chapel chimney.
In St. Peter's Square, the stormy clouds parted, making way for a rare dose of sunshine. It was perfect timing as the masses began showing up. Anticipating that historic moment is a common bond shared by everyone, including the media, tourists and police.
Inside the basilica Tuesday morning, cardinals celebrated a final day of mass. The homily was by Cardinal Antelo Sodano, who delivered a message of love, unity and the mission of the new pope.Check out 7 Fun Facts about the history of the secret, mystical process of the conclave.
The cardinals then headed to the Sistine Chapel with a solemn procession, where they took an oath of secrecy surrounded by Michelangelo's imposing frescoes. It was preceded by a final appeal for unity to heal the divisions that have been exposed by Pope Benedict XVI's shocking resignation and revelations of corruption and mismanagement in the Vatican bureaucracy.
Outside, thousands of people braved cold night rain and packed St. Peter's Square, eyes fixed on the narrow chimney poking out of the Sistine Chapel roof. They were rewarded some three hours after the conclave began when thick black smoke billowed out of the chimney, signaling that no pope had been elected.
There are still no clear frontrunners, only speculation and favorites, including U.S. cardinals Timothy Dolan of New York and Sean Patrick O'Malley of Boston.
Dolan wrote in a letter to his priests that he predicts there will be a new pope by Thursday evening, with the inaugural mass taking place on March 19.
The longest conclave held since the turn of the 20th century lasted five days. If a pope is not elected in the first four days of voting, the cardinals will pause on the fifth day to pray, talk and listen to a brief speech given by the senior cardinal in the order of deacons.
As the conclave to elect the next pope begins, Catholics all over the world are holding prayer vigils to help guide the cardinals in their decision.
In downtown Los Angeles, the Cathedral of Our Lady of the Angels hosted an overnight 12-hour prayer vigil. Several hundred parishioners gathered for the start of the vigil at 7 p.m. Monday. Every hour throughout the night, there was a recitation of the rosary and other prayers to support the cardinals.
On Tuesday, the cardinals were set to head off to breakfast around 7:30 a.m., mass at 8:30 a.m. and then back inside the Sistine at 9:30 a.m. We can expect two votes in the morning and two votes in the afternoon. The first plume of smoke should be seen early in the afternoon and the second, if necessary, in the early evening.