Pope Benedict shocked the world on Monday by saying he no longer had the mental and physical strength to cope with his ministry, in an announcement that left his aides "incredulous" and will make him the first pontiff to step down since the Middle Ages.
The German-born Pope, 85, admired as a hero by conservative Roman Catholics and viewed with suspicion by liberals, told cardinals in Latin that his strength had deteriorated recently.
He will step down on Feb 28 and the Vatican expects a new Pope to be chosen by the end of March.
Vatican spokesman Father Federico Lombardi said the Pope had not decided to resign because of "difficulties in the papacy" and the move had been a surprise, indicating that even his inner circle was unaware that he was about to quit.
The Pope does not fear schism in the Church after his resignation, the spokesman said.
The Pope's leadership of 1.2 billion Catholics has been beset by child sexual abuse crises that tarnished the Church, one address in which he upset Muslims and a scandal over the leaking of his private papers by his personal butler.
The pope told the cardinals that in order to govern "...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.
{{/usCountry}}The pope told the cardinals that in order to govern "...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.
{{/usCountry}}"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."
He also referred to "today's world, subject to so many rapid changes and shaken by questions of deep relevance for the life of faith."