The pope is to resign his office after declaring he was too old to carry on as head of the Catholic Church.
Pope Benedict XVI will quit on February 28, the Vatican said today, adding the announcement was a surprise.
A Vatican statement said the pope was unable to continue in office due to his age and diminishing strength, he is 85, and the papacy will remain vacant until a successor is elected.
He is the first pontiff to resign in nearly 600 years. The decision sets the stage for a conclave to elect a new pope before the end of March.
The pope announced his decision in Latin during a meeting of Vatican cardinals this morning.
"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," he told the cardinals.
"I am well aware that this ministry, due to its essential spiritual nature, must be carried out not only by 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 St. Peter and proclaim the Gospel, both strength of mind and body are necessary - strengths which in the last few months, has deteriorated in me to the extent that I have had to recognise my incapacity to adequately the ministry entrusted to me."
The last pope to resign was Pope Gregory XII, who stepped down in 1415 in a deal to end the Great Western Schism among competing papal claimants.
The pope called his choice "a decision of great importance for the life of the church."
There are several papal contenders in the wings, but no obvious front-runner as was the case when Pope Benedict was elected pontiff in 2005 after the death of Pope John Paul II.
Giving his reaction the resignation, Bishop of Lancaster Michael Campbell said: "The news of Pope Benedict XVI’s impending resignation at the end of February will have come as a shock and a cause of sadness to many Catholics and to numerous others, believers and non-believers alike.
"The burden of the Petrine office is a heavy one and the Church can be immensely grateful for the willingness of Cardinal Joseph Ratzinger in assuming such a responsibility at his age in 2005.
"We can but admire his courage in deciding that he no longer possesses the physical and mental strength to continue as the successor of Peter.
"Since his election the Holy Father has carried out his papal duties with devotion and dignity, and employed his many gifts, not least those of a fine intellect, as supreme pastor of the Church.
"Catholics in England and Scotland recall with pleasure and pride, as well as
gratitude, his recent visit to these islands and the powerful impact for good his presence had on so many of our fellow-citizens.
"Being Pope, with concern for all the churches as St. Paul expressed it, has never been easy.
"History will record the years of Pope Benedict’s papacy as particularly difficult and trying ones for the Church.
"Equally, his prayerfulness and quiet dignity brought a sense of God’s calm and reassurance to believers in often troubled times.
"We thank God for the blessing that Pope Benedict has been to the Church and to the world, and we will accompany him in prayer as he moves into retirement and the promise of quieter days.
"On this Feast of Our Lady of Lourdes we commend the Holy Father to the loving care and maternal protection of Our Blessed Lady, the Mother of our saviour."