Roman Catholic cardinals from around the world are due to meet in Rome to begin the process of electing the next Pope.
The College of Cardinals will hold daily talks leading up to a conclave in which a new Pope will be chosen.
The election process comes after Pope Benedict XVI stepped down after nearly eight years in office leading the world’s 1.2 billion Roman Catholics.
He was the first pontiff to resign in 600 years.
The first pre-conclave meeting on Monday morning is to be headed by the dean of the College of Cardinals, Cardinal Angelo Sodano.
Cardinals – known as the “princes” of the Church – will discuss future challenges to the Church and discreetly weigh up possible papal candidates.
The conclave – to be held in the Sistine Chapel – is expected to take place next week.
Correspondents say the 115 cardinal electors, those under the age of 80 who will take part in the conclave, will want the new Pope to be officially installed in time to preside over Holy Week.
Ceremonies start with Palm Sunday on 24 March and culminate in Easter the following Sunday.
The BBC’s David Willey in Rome says strict precautions against leaks of unauthorised information will be in operation at the Vatican until the next Pope has been chosen.
Technicians will debug the cardinals’ lodgings and mobile phones will be banned altogether during the conclave.
Britain’s formerly most senior Roman Catholic cleric, Cardinal Keith O’Brien, has said he will not take part in the conclave after standing down amid allegations of improper behaviour.
On Sunday, he admitted his sexual conduct had at times “fallen beneath the standards expected of me”.
He apologised and asked forgiveness from those whom he had “offended”.
Cardinal O’Brien resigned as Archbishop of St Andrews and Edinburgh last Monday after three priests and a former priest made allegations against him dating back to the 1980s.
Benedict, 85, officially ceased to be the Pope at 20:00 local time (19:00 GMT) on Friday.
He left the Vatican in a motorcade before being flown by helicopter to the papal retreat at Castel Gandolfo, near Rome.
He has vowed “unconditional obedience and reverence” to his successor.
The German pontiff, who was born Joseph Ratzinger, will continue to be known as Benedict XVI, with the new title of “pope emeritus”.
The theologian is expected to retire to a monastery on a hill inside Vatican City. Officials say he will not be able to intervene publicly in the next papacy although he may offer advice.