Pope Benedict XVI has announced he is to resign at the end of February.
The 85-year-old Roman Catholic Church leader, Joseph Ratzinger, said he is to step down on February 28.
The Pope admitted he no longer had the "strength" to go on as the leader of the world's one billion Catholics.
"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.
"It is for the Church's good. I feel the burden of my duty."
"[I'm] fully aware of the gravity of this gesture.
Ratzinger, who was elected pope on 19 April 2005 by a papal conclave, made the announcement of his intention to retire in Latin during a consistory for the canonisation of Otranto's martyrs.
The Pope said his mind and body strength had severely deteriorated in the last months.
"I have had to recognise my incapacity to adequately fulfil the ministry entrusted to me," the Pope said.
Ratzinger's elder brother, Georg, said doctors recently told the Pope not to take transatlantic trips for health reasons.
Angelo Sodano, the Dean of the College of Cardinal Angelo Sodano, said the news came "as a bolt out of the blue," Italian news agency Ansa reported.
The last pope to resign was Pope Gregory XII in 1415.
Born in Marktl, Bavaria, Ratzinger is the sixth German to serve as pope and succeeded to Poland native John Paul II.
Follow our live blog on the Pope's resignation here.