The 117 cardinals who will elect the successor to the late Pope John Paul are the most powerful men in Roman Catholicism and their College of Cardinals the Church's most exclusive club.
Following are some facts about cardinals:
What are they?
Cardinals, often referred to as the "princes of the Church", are the closest advisers to the Pope and are personally named by him. They are usually archbishops of major dioceses or heads of influential agencies at the Vatican.
They outrank all other clergy besides the Pope. The word cardinal comes from the Latin cardo (hinge) and and symbolises the link they assure between the Vatican and major dioceses around the world. Their trademark red hat stands for their readiness to shed their blood for the Church.
What do they do?
The cardinals' most important job is electing a papal successor from among their own ranks in a conclave after the death of a Pontiff. Only those under the age of 80 are eligible to participate. As the Pope's top advisers, they help him govern by serving on Vatican congregations and councils, the equivalent of government ministries.
Powerful cardinals frequently sit on several of these congregations and councils. Those who are archbishops also run large dioceses such as capital cities.
How to get the red hat
The Pope occasionally names a group of new cardinals to replace those who have retired or died and to reward bishops for their achievements. Pope John Paul's last consistory in October 2003, the ninth during his papacy, elevated 31 new cardinals.
The honour can come with the job of running a prominent archdiocese or be given in recognition of personal achievement. There are 183 cardinals around the world but only 117 of them are under 80 years old and thus eligible to vote in the conclave. The maximum number of cardinal electors is set by Church law at 120.
Pope John Paul named one cardinal in secret in 2003 but he will not be able to join the cardinals - if he is under 80 - because his name was not made public before the Pope died.
Popes sometimes name a cardinal in secret to protect him from possible reprisals in a country that oppresses the Church.
The Pope has himself appointed all but two of the 117 cardinal electors. They hail from five continents and 53 different countries. The majority - 77- run an archdiocese while 23 work in the Curia and 17 have no official post.
Of the 117, 58 are from Europe (including 20 Italians), 21 from Latin America, 14 from North America, 11 from Africa, 11 from Asia and two from Oceania.
Their average age is 71 years old.
And who will be the next Pope?
There are no official candidates and cardinals are forbidden by Church law to discuss the issue in public. They are also banned from revealing details of the discussions and voting inside the locked Sistine Chapel where their conclave meets.
Vatican watchers avidly swap and update lists of papabile ("pope-ables") based on cardinals' activities, comments about them from other prelates and pure speculation.
Known as "vaticanistas", these observers regularly fill Italian newspapers with the latest information and gossip on who's ahead and who's behind in the papal sweepstakes.
Dublin bookmaker Paddy Power takes bets and gives odds on more than two dozen leading candidates for the papacy.