The first pope to resign in 600 years, Benedict XVI has told Catholics he will live out his life "simply a pilgrim." He left the Vatican and flew to the papal summer residence of Castel Gandolfo to remove his ring.
At 1900 GMT, Benedict XVI ceased to be pope.
"Thank you for your love and support," Benedict wrote in his final tweet. "May you always experience the joy that comes from putting Christ at the centre of your lives."
The 85-year-old shocked the world earlier this month, becoming the first pontiff to step down of his own free will in 600 years. He cited his advancing age and declining strength as reasons for his resignation.
The Pope's unprecedented decision has raised many questions about what role he will assume and how his life will look in the future.
He will receive two new titles - Roman pontiff emeritus and emeritus pope - but will continue to be addressed directly as "Your Holiness."
The College of Cardinals is scheduled to meet early next week to discuss the current priorities for the church and to set the date for the conclave where the next pope will be elected.
Addressing tens of thousands of pilgrims gathered at the Vatican on the eve of his resignation on Wednesday, Pope Benedict XVI gave an emotional farewell.
"Right now my soul is open to embrace the entire Church and I'd like to thank everybody for the help I have received and the charity that's inside the church," he said, adding that he never felt alone in such a public position.
mkg/dr (AFP, Reuters, AP, dpa)