Benedict has dealt with health issues for some time, and the 85-year-old announced his decision in Latin during a meeting of Vatican cardinals Monday morning, according to the Associated Press. The move took almost all Vatican observers, and millions of Catholics around the world, by surprise.
He said that because of his advanced age and diminishing strength, he didn't feel he could carry on the job. Reuters quoted the Pope as saying he was "fully aware of the gravity" of his resignation.
The pope's brother, Georg Ratzinger, told a news agency in Germany that the pontiff had been advised by his doctor not to take any more transatlantic trips and had been considering stepping down for months.
Talking from his home in Regensburg to the news agency dpa, Georg Ratzinger said his brother was having increasing difficulty walking and that his resignation was part of a "natural process."
"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."
The 265th Pontiff, Benedict will be the first leader of the Church to step down voluntarily in almost six centuries. He has led the Church since 2005 through a tumultuous time that has seen him criticized for his handling of the scandal related to years of sexual abuse of young parishioners by priests and other clergy, and senior church officials' alleged moves to hide those actions.
Benedict's decision sets the stage for a conclave to elect a new pope before the end of March.
The following is a transcription of part of the remarks Pope Benedict made in Latin to his cardinals on Monday morning, which was released to the media by the Vatican (Click here to read the full text):
"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 recognize my incapacity to adequately fulfill the ministry entrusted to me."