Vatican City - Only a few of the 115 cardinal electors taking part in the conclave starting on Tuesday are considered pontiff material, or "papabile".
Here are some of the top contenders to become the next head of the world's 1.2 billion Catholics, as cardinals gather in the Sistine Chapel:
The 71-year-old archbishop of Milan is a keen promoter of inter-religious dialogue, particularly between Muslims and Christians.
He is also an expert on bioethics, an issue on which Roman Catholic Church teachings are currently lagging behind scientific advances.
The son of a socialist truck driver, Scola is one of the closest heirs to Benedict XVI, combining conservative views with progressive social advocacy on issues like immigration and poverty.
He is Italian but is not associated with the Vatican bureaucracy, whose image has been badly tarnished by infighting in recent years.
The 63-year-old Brazilian is archbishop of Sao Paolo, home to five million faithful in a country that has the world's biggest Catholic population.
Scherer, whose family descended from German immigrants, is seen as a moderate conservative with charisma and openness, as well as a good administrator.
He has fought against declining traditional values and is concerned about the growing strength of evangelical churches across the developing world.
Scherer is well acquainted with social problems in Sao Paulo, a cosmopolitan city of 11 million people facing high poverty rates, crime, youth unemployment and lack of basic services.
On his archdiocesan website and in newspapers, Scherer regularly offers commentary on key issues. He is also very active on Twitter, boasting 20 000 followers of his account @DomOdiloScherer.
Canada's former archbishop of Quebec, aged 68, Ouellet now heads the influential Congregation of Bishops and is seen as the leading North American candidate for the papacy.
Known for his conservative theological views - very much in line with Benedict's - Ouellet could be favoured for the pull he may have in the increasingly secularised West.
Supporters hope he would also crack down on the unruly Curia, the Vatican's government. He is the head of the Pontifical Commission for Latin America, where he has a strong following.
The mainstream conservative churchman who once said becoming pope "would be a nightmare" is an insider with strong connections to the Curia.
Branded the "Iron Cardinal" by Canadian media for his buttoned-down views, Ouellet could widen a rift between conservatives and reformists, according to Gilles Routhier, head of Laval University's theology faculty in Quebec City.
Archbishop of Budapest since 2002 and a canon law expert who has taught at the Pontifical Lateran University in Rome, the 60-year-old Hungarian is known for his efforts to combat secularisation.
The archbishop of Vienna, aged 68, has called for a re-examination of the issue of priest celibacy in the wake of the child sex abuse scandal.
The Austrian has also criticised powerful figures in the Vatican for covering up the sex crimes.
Jose Francisco Robles Ortega
The 64-year-old archbishop of Guadalajara, Mexico's second largest city, is described as reserved and lacking charisma.
He has taken a stand against the rampant violence linked to drug traffickers in his country, as well as rising secularism.
Luis Antonio Tagle
The archbishop of Manila was last year appointed the Church's second youngest cardinal. The 55-year-old is tipped as an outsider to watch for his dynamism, charisma and stellar rise.
His relative youth stands against him, but he is very popular in Asia and has worked closely with Benedict.
Archbishop of New York and a "modernist conservative", 63-year-old Dolan is media savvy - a plus in today's social media society.
Vatican experts say his strong point lies in heading up a diocese on the front-line of sex abuse scandals, but activists have criticised him for allegedly covering up cases.
The staunchly pro-life archbishop of Boston, aged 68, is a member of the Capuchin order who became the first cardinal with a blog in 2006.
He has vowed a zero-tolerance policy against sexual abuse by priests and settled dozens of claims.
South African Cardinal Wilfrid Fox Napier is the 71-year-old archbishop of Durban who has said the Church is in a "profound crisis" and needs a new pope to implement "spiritual renewal".