Pope Benedict XVI is to resign at the end of this month in an unexpected development, saying he is too old to continue at the age of 85.
He became Pope in 2005 following John Paul II's death.
Resignations from the papacy are not unknown, but this is the first in the modern era, which has been marked by pontiffs dying while in office.
At 78, the former Cardinal Joseph Ratzinger was one of the oldest new popes in history when elected.
The BBC's Alan Johnston in Rome says the news has come "out of the blue", and that there was no speculation whatsoever about the move in recent days.
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POPE BENEDICT XVI
* At 78, one of the oldest new popes in history when elected in 2005
* Born in Germany in 1927, joined Hitler Youth during WWII and was conscripted as an anti-aircraft gunner but deserted
* As Cardinal Joseph Ratzinger spent 24 years in charge of Congregation for the Doctrine of the Faith - once known as the Holy Office of the Inquisition
* A theological conservative, with uncompromising views on homosexuality and women priests
He took the helm as one of the fiercest storms the Catholic Church has faced in decades - the scandal of child sex abuse by priests - was breaking.
The Vatican says it expects the period between the Pope's resignation and the election of his successor to be as brief as possible, but there has been no confirmation on when cardinals will meet to choose a new pontiff.
In a statement, the pontiff said: "After having repeatedly examined my conscience before God, I have come to the certainty that my strengths, due to an advanced age, are no longer suited to an adequate exercise of the Petrine ministry.
"I am well aware that this ministry, due to its essential spiritual nature, must be carried out not only with words and deeds, but no less with prayer and suffering.
"However, in today's world, subject to so many rapid changes and shaken by questions of deep relevance for the life of faith, in order to govern the bark of Saint Peter and proclaim the Gospel, both strength of mind and body are necessary, strength which in the last few months, has deteriorated in me to the extent that I have had to recognise my incapacity to adequately fulfil the ministry entrusted to me.
"For this reason, and well aware of the seriousness of this act, with full freedom I declare that I renounce the ministry of Bishop of Rome, Successor of Saint Peter, entrusted to me by the Cardinals on 19 April 2005, in such a way, that as from 28 February 2013, at 20:00 hours, the See of Rome, the See of Saint Peter, will be vacant and a Conclave to elect the new Supreme Pontiff will have to be convoked by those whose competence it is."
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