Pope Benedict left the Catholic world in shock after becoming the first pontiff since the Middle Ages to resign his office, saying that failing strength had left him unable to lead the church through a period of relentless change and turmoil.
The 85-year-old pontiff announced his abdication as leader of the world's 1.2 billion Catholics in a speech delivered in Latin, the universal language of the church, to cardinals meeting in the Vatican's Apostolic Palace.
"I have come to the certainty that my strengths, due to an advanced age, are no longer suited to the adequate exercise of the Petrine ministry," he said, referring to the tradition that dates the papacy back to Saint Peter, 2,000 years ago.
He will continue in office until 1900 GMT on Feb. 28 before stepping down to allow the election of a new pope, which Vatican officials said was expected to come by the start of the Holy Week on March 24.
(Read More: Next Pope? Ghana Cardinal Turkson Takes Lead )
He is expected to spend some time at the pope's summer residence near Rome before retiring to spend his final years in a cloistered convent in the Vatican, and will play no part in selecting his successor.