Pope Benedict XVI announced Monday he will step aside as leader of the world's 1.2 billion Roman Catholics on Feb. 28, saying he no longer has the strength to carry out his duties.
Speaking in Latin, the 85-year-old announced his decision during an address at the "Concistory for the canonization of the martyrs of Otranto", a small event held early in the morning.
The decision makes him the first pope to resign since the Middle Ages.
His statement was posted on the Vatican Radio website. Carrying out the duties of being pope required "both strength of mind and body," it said.
NBC New Vatican analyst George Weigel gives his thoughts on Pope Benedict XVI's announcement of his resignation, and explains how a new pope will be selected.
"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 pontiff's statement said.
The choice was a "decision of great importance" for the church, the statement added.
German news agency dpa quoted the pontiff's brother, Georg Ratzinger, as saying his brother was increasingly struggling to walk and had been contemplating stepping aside for several months. "His age is weighing on him," he reportedly added.
There are several papal contenders in the wings, but no obvious front-runner, The Associated Press reported. It added:
Contenders to be his successor include Cardinal Angelo Scola, archbishop of Milan, Cardinal Christoph Schoenborn, the archbishop of Vienna, and Cardinal Marc Ouellet, the Canadian head of the Vatican's office for bishops.
Reuters quoted a Vatican spokesman as saying the pontiff did not fear schism in the Church following his resignation.
Luke Coppen, editor of UK newspaper The Catholic Herald, told the Daily Telegraph: "Pope Benedict's pontificate has been full of surprises. This is the biggest one of all."