The last Pope to resign willingly was Celestine V, who stepped down in 1294, while Gregory XII reluctantly abdicated in 1415.

BBC: News Online

Pope Gregory XII - who reigned from 1406 to 1415 - did so to end what was called the Western Schism.

BBC: How does a Pope resign from office?

But resignation is extremely rare: the last pontiff to step aside was Pope Gregory XII, who resigned in 1415 amid a schism within the Church.

BBC: Pope Benedict has a pacemaker, the Vatican confirms

ROME Whatever challenges the Roman Catholic Church faces in 2013, they pale compare to those that prompted the resignation 598 years ago of Pope Gregory XII.

WSJ: When Last Pope Retired, Church Was in Turmoil

The last pope to resign was Pope Gregory XII, who stepped down in 1415 in a deal to end the Great Western Schism among competing papal claimants.

NPR: Pope Resigning On Feb. 28, Conclave In March

There were three rival claimants to the papal throne at that time - the Roman Pope Gregory XII, the Avignon Pope Benedict XIII, and the Antipope John XXIII.

BBC: How does a Pope resign from office?

The last pope to resign was Gregory XII in 1415.

CNN: Pope Benedict to resign at the end of the month, Vatican says