The pope has announced his resignation saying at 85 he was too old and infirm to carry on.
Pope Benedict XVI will resign on February 28, the first pontiff to do so in nearly 600 years. His 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.
He emphasised that carrying out the duties of being pope - the leader of more than a billion Roman Catholics worldwide - requires "both strength of mind and body."
"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 barque 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 fulfil the ministry entrusted to me."
The last pope to resign was Gregory XII in 1415 as part of a deal to end the Great Western Schism among competing papal claimants.
Benedict called his choice "a decision of great importance for the life of the church." The move sets the stage for the Vatican to hold a conclave to elect a new pope by mid-March, since the traditional mourning time that would follow the death of a pope does not have to be observed.
Benedict himself raised the possibility of resigning if he were simply too old or sick to continue on in 2010, when he was interviewed for the book "Light of the World." "If a pope clearly realises that he is no longer physically, psychologically and spiritually capable of handling the duties of his office, then he has a right, and under some circumstances, also an obligation to resign," Benedict said.
The pope's brother, Georg Ratzinger, said the pontiff had been advised by his doctor not to take any more transatlantic trips and had been considering stepping down for months. Georg Ratzinger said his brother was having increasing difficulty walking."His age is weighing on him," the 89-year-old said of his 85-year-old brother. "At this age my brother wants more rest."