An illuminating view of Church history...
"Popes Who Resigned (reprinted from America Magazine, February 28, 2005)
Historical evidence for papal resignations is limited, especially if one eliminates resignations that may have been forced.
1. Clement I (92?-101). Epiphanius asserted that Clement gave up the pontificate to Linus for the sake of peace and became pope again after the death of Cletus.
2. Pontian (230-235). Allegedly resigned after being exiled to the mines of Sardinia during persecution of Maximinus Thrax.
3. Marcellinus (296-304). Abdicated or was deposed after complying with Diocletian?s order to offer sacrifice to pagan gods.
4. Martin I (649-655). Exiled by Emperor Constans II to the Crimea. Before he died, the clergy of Rome elected a successor, whom he appears to have approved.
5. Benedict V (964). After one month in office, he accepted deposition by Emperor Otto I.
6. Benedict IX (1032-45). Benedict resigned after selling the papacy to his godfather Gregory VI.
7. Gregory VI (1045-46). Deposed for simony by Henry III.
8. Celestine V (1294). A hermit, elected at age of 80 and overwhelmed by the office, resigned. He was imprisoned by his successor.
9. Gregory XII (1406-15). Resigned at request of Council of Constance to help end the Great Western Schism.
Source: Patrick Granfield, ?Papal Resignation? (The Jurist, winter and spring 1978) and J. N. D. Kelly, The Oxford Dictionary of Popes (1986). "