The 85-year-old pope announced his decision in Latin during a meeting of Vatican cardinals Monday 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 spiriual 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 recognize my incapacity to adequately the ministry entrusted to me."
Benedict called his choice "a decision of great importance for the life of the church."