Resignation is possible under Canon Law
Pope Benedict XVI. is only the second pope, who is retiring in about two millennia of Church history. Coelestin V. had previously resigned in 1294, after only a few months in office voluntarily. He died in captivity in 1296 .
A pope is elected for life, but according to canon law, a resignation is also possible . The head of the church does not even require to give reasons. Also, no one needs to accept the resignation specifically. It is crucial, however, that the decision to withdraw is entirely voluntary. The in 1983 by John Paul II reformed Canon Law (Can. 332nd Clause 2) states: “If it happens that the Roman Pontiff resigns his office, it is required for validity that the resignation is made freely and properly manifested but not that it is accepted by anyone.”
However, before Pope Benedict XVI there is known only one voluntary resignation. Pope Coelestin V. left office Voluntarily on December 13 1294 after only five months. He was overwhelmed. Church historians speak of an unprepared and uneducated hermit who could barely speak Latin. The Cardinals had just elected him pope, because in nearly two years of struggle they could not agree on another competent candidate. Coelestin retired to a monastery after resigning.