Pope Benedict XVI will resign on Feb. 28, the Vatican says.
In a statement posted on Vatican Radio's website, the 85-year-old Pope said his health was the reason the surprise announcement.
"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," the Pope said.
Benedict said his strength, over 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."
The resignation means there will be no Pope until a successor is picked, the Vatican said.