The 85-year-old German-born Pope, hailed as a hero byconservative Catholics and viewed with suspicion by liberals, saidhe had noticed that his strength had deteriorated over recentmonths.
A Vaticanspokesman said the Pope had not resigned because of "difficultiesin the papacy" and the decision had been a surprise, indicatingthat even his closest aides were unaware that he was about to quit.The Pope does not fear schism in the Church after his resignation,the spokesman said.
The Pope'sleadership of 1.2 billion Catholics has been beset by a childsexual abuse crisis that tarnished the Church, one address in whichhe upset Muslims and a scandal over the leaking of his privatepapers by his personal butler.
In a statement,the pope said in order to govern "...both strength of mind and bodyare necessary, strength which in the last few months, hasdeteriorated in me to the extent that I have had to recognise myincapacity to adequately fulfil the ministry entrusted tome.
"For this reason,and well aware of the seriousness of this act, with full freedom Ideclare that I renounce the ministry of Bishop of Rome, Successorof Saint Peter."
Before he waselected Pope, the former Cardinal Joseph Ratzinger was known bysuch critical epithets as "God's rottweiler" because of his sternstand on theological issues.
But after severalyears into his new job he showed that he not only did not bite butbarely even barked.
In recent months,the Pope has looked increasingly frail in public sometimes beinghelped to walk by those around him.
A Vaticanspokesman said the pontiff would step down from 1900 GMT on Feb.28, leaving the office vacant until a successor was chosen toBenedict who succeeded John Paul, one of history's most popularpontiffs.