From left, Cardinals Luis Aponte Martinez of Puerto Rico, Georg Maximilian Sterzinsky of Germany and Geraldo Majella Agnelo of Brazil
The cardinals will be cut off from the outside world during their conclave. In fact, the word conclave is Italian meaning "with key," and the cardinals literally lock themselves in during the voting.
The 115 cardinals, who are under 80 years of age, meet in closed deliberations to vote for who will become the next pope by secret ballot. They vote once at the start of the conclave and twice a day thereafter until one person receives the two-thirds majority required.
If after more than a week of deliberating a pope has not been chosen, the cardinals may agree to elect the first candidate who reaches a simple majority.
Church members believe the Holy Spirit will guide the selection of a pope. Therefore, electors are forbidden from making agreements for or against a candidate, and cannot be swayed by outside forces or even their personal opinions.
Cardinals Walter Kasper says, "A pope can only come from the middle field because it's a task of the pope to be responsible for the unity of the church and you cannot go to one or the other extreme otherwise you will divide the church. "
Cardinal Gotfried Daneels adds, "I think the Cardinals are very clearly looking for what their conscience dictates for the new one who has to come. I don't think it has any influence at all. They will freely decide. They are intelligent people."
Many cardinals declined to speak to the media in the days leading up to the conclave.
Cardinal Christoph Schoenborn says, "It's not the time to give interviews, it's the time to pray and say thanks to the great Holy Father for this great pope and what he as given to us and to the whole world."
That's Cardinal Christoph Schoenborn of Austria, who is considered one possibility for the papacy.
Another is Cardinal Francis Arinze, of Nigeria, who has worked as a mediator between Catholicism and other major religions. If chosen, he would be the first black pope in modern times.
There's also German Cardinal Joseph Ratzinger, a conservative, who is the head of a Vatican office, which oversees and enforces church doctrine.
And Cardinal Claudio Hummes, the archbishop of Sao Paulo, Brazil, leads the Catholics in the biggest city in South America.
Vatican watchers say a Hummes papacy would energize Catholic Latin Americans.
That might also be the case if Cardinal Oscar Rodriguez Maradiaga of Honduras is chosen.
Italy provided popes for the 455 years before John Paul II was chosen in 1978. Among the Italians, Cardinal Dionigi Tettamanzi of Milan is often mentioned. But he lacks international experience.
But as history has proven, the conclave could choose someone relatively unknown, as it chose Cardinal Karol Wojtyla in 1978, who took the name John Paul II.