A new pope is elected by the College of Cardinals in Vatican City, who gather under Michelangelo's famous frescoes in the Sistine Chapel under strict security measures. Only cardinals under the age of 80 can vote, which means 118 members are eligible to vote for Pope Benedict's successor.
This process is called a conclave and it will take place at the end of March to elect a new pope in place of Benedict XVI, who announced today he is stepping down.
The cardinals are totally cut off from the outside world during conclave as television, phones, newspapers and computers are all banned. The cardinals are housed in private rooms in the Santa Maria house until a new pope is elected.
Aside from the cardinals, about 70 other people are allowed in the Santa Maria house such as doctors, cooks and housekeepers.
Each voting cardinal writes the name of his choice for pope on a ballot and is asked to disguise his handwriting to avoid letting others know who is supporting whom.
If no one receives the required two-thirds-plus-one votes, additional ballots take place immediately. There can be only four ballots in a single day, and if after three days the cardinals still haven't selected anyone, the voting sessions can be suspended for a day of prayer and discussion.
Rules indicate that any unmarried Catholic male can be elected as the new pope. Though, for more than 1,000 years, it's almost always been a cardinal. It's not clear whether Pope Benedict will play any role in the proceedings.
In 1800, the balloting conclave lasted three and a half months, and in 1831, 54 days, but in modern times, conclaves usually last, at most, only a few days.
When the votes do finally tally up for one man, he is asked by the Dean of Cardinals if he will accept and if he does, he is asked by what name he wishes to be called.
After the cardinal deacon announces "Habemus Papam" to the crowds outside - Latin for "We have a pope." The new Pope appears and gives his first message to the world.
If no pope is chosen, the ballots are burned with chemical pellets to produce black smoke from a chimney on the roof of the Sistine Chapel. If the cardinals elect a new pope, white puffs of smoke -- or fumata bianca in Italian -- are sent from the chimney.