Pope Benedict's resignation has been greeted with surprise, admiration and disappointment from around the world.
Catholic bishops from Brazil - the world's largest Catholic country - issued a statement hailing the Pope's "humility and greatness".
"We greet with filial love the reasons given by his holiness, sign of the humility and greatness which characterized the eight years of his pontificate."
In Germany, the country of the former Cardinal Joseph Ratzinger's birth, the news was greeted with surprise.
Max Seckler, a retired theology professor who worked with Ratzinger at Germany's University of Tuebingen in the 1960s first thought the news was a joke.
"I didn't expect it, but it was something I wouldn't have put past him," Seckler. "He was in many aspects of his papacy very innovative and unconventional."
The newly-elected head of the Church of England, Archbishop of Canterbury Justin Welby, said Pope Benedict brought a "remarkable and creative theological mind to bear on the issues of the day".
"As I prepare to take up office I speak not only for myself, and my predecessors as Archbishop, but for Anglicans around the world, in giving thanks to God for a priestly life utterly dedicated, in word and deed, in prayer and in costly service, to following Christ," he said in a statement.
Israeli President Shimon Peres said he was "saddened" to hear of Benedict's departure.
"Under his leadership the Vatican has been a clear voice against racism and anti-Semitism and a clear voice for peace. Relations between Israel and the Vatican are the best they have ever been and the positive dialogue between the Catholic Church and the Jewish people is a testament to his belief in dialogue and cooperation," Peres said.
However the conservative pope is not without his critics. The Survivors Network of those Abused by Priests, which has 12,000 members worldwide, accuse Benedict of choosing to protect the reputation of the church over the welfare of children.
"Before he became Pope his predecessor put him in charge of the abuse crisis. He has read thousands of pages of reports of the abuse cases from across the world. He knows more about clergy sex crimes and cover-ups than anyone else in the church yet he has done precious little to protect children," David Clohessy, executive director of SNAP told the Guardian.
US President Barack Obama was among many world leaders who iissued a statement after the announcement.
"On behalf of Americans everywhere, Michelle and I wish to extend our appreciation and prayers to His Holiness Pope Benedict XVI. Michelle and I warmly remember our meeting with the Holy Father in 2009, and I have appreciated our work together over these last four years. The Church plays a critical role in the United States and the world, and I wish the best to those who will soon gather to choose His Holiness Pope Benedict XVI's successor."
British Prime Minister David Cameron also thanked Pope Benedict in a statement.
"I send my best wishes to Pope Benedict following his announcement today. He has worked tirelessly to strengthen Britain's relations with the Holy See. His visit to Britain in 2010 is remembered with great respect and affection. He will be missed as a spiritual leader to millions."
French President Francois Hollande said Benedict's decision to leave the role "stirs the greatest respect" and praised the pope "for all the efforts he led in support of peace".
"It's a courageous and exceptional decision," he said.
- Herald Online, AP, AFP