This April 24, 2005 file photo shows thousands of people attending the installment Mass of Pope Benedict XVI in St. Peter's Square, at the Vatican.Gregorio Borgia/The Associated Press
Pope Benedict XVI's resignation sets in motion a complex sequence of events to elect the next leader of the Roman Catholic Church. The laws governing the selection after a pope's resignation are the same as those in force after a papal death, aside from skipping a period of mourning.
The Vatican summons a conclave of cardinals that must begin 15 to 20 days after Benedict's Feb. 28 resignation.
Cardinals eligible to vote – those under 80 years old – are sequestered within Vatican City and take an oath of secrecy.
There are currently 118 cardinals under 80 and eligible to vote, 67 of whom were appointed by Benedict. However, four of them will turn 80 before the end of March. Depending on the date of the conclave, they may or may not be allowed to vote.
Any baptized Roman Catholic male is eligible for election as pope, but only cardinals have been selected since 1378.
Two ballots are held each morning and two each afternoon in the Sistine Chapel. A cellphone scrambler sits underneath the raised floor. A two-thirds majority is required. Benedict in 2007 reverted to this two-thirds majority rule, reversing a 1996 decision by Pope John Paul II, who had decreed that a simple majority could be invoked after about 12 days of inconclusive voting. Benedict did so to prevent cardinals from holding out for 12 days then pushing through a candidate who had only a slim majority.
Each cardinal writes one name under the Latin words, "Eligo in Summum Pontificem" (I elect as Supreme Pontiff). At the altar, each cardinal places his ballot on a plate covering an urn, and tilts it so the ballot slides into the urn.
Ballots are burned after each round. Black smoke means no decision; white smoke (created by adding chemicals) signals that cardinals have chosen a pope and he has accepted. Bells also signal the election of a pope to help avoid possible confusion over the colour of smoke coming from the Sistine Chapel chimney.
The new pope then chooses his papal name. He is introduced from the loggia overlooking St. Peter's Square with the words "Habemus Papam!" (Latin for "We have a Pope!") and he then imparts his first blessing.