Upon the pope's death, the cardinals of the Catholic Church who were in Rome met and set a date for the beginning of the conclave.

Of the 117 eligible members of the College of Cardinals, those younger than 80 years of age at the time of the death of Pope John Paul II, all but two attended.

Pope John Paul II laid out new procedures for the election of his successor in his Apostolic Constitution Universi Dominici gregis in 1996.

He maintained the rule established by Paul VI that cardinals who reached the age of eighty before the day the pope died would not participate in the balloting.

[2] John Paul kept the voting in the Sistine Chapel, but provided for the cardinal electors when not balloting to live, dine, and sleep in air-conditioned individual rooms in Domus Sanctae Marthae, better known by its Italian name Casa Santa Marta, a five-story building, completed in 1996, that normally serves as a guesthouse for visiting clergy.

Poor health prevented two of the 117 cardinal electors from attending: Jaime Sin of the Philippines and Adolfo Antonio Suárez Rivera of Mexico.

Celebrants included Bernard Law, Camillo Ruini, Jorge Medina, Eugênio de Araújo Sales, Nasrallah Pierre Sfeir, Leonardo Sandri, and Piergiorgio Silvano Nesti.

[11][8] In La Repubblica, veteran journalist Gad Lerner wrote that preventing "public reflection" by the cardinals "mutes their relationship to the world", deprives them of a "beneficial antidote to excessive scheming", and increased the influence of the Curia.

The preacher was Raniero Cantalamessa, a Capuchin friar and Church history scholar, who had for several years preached the Lenten sermons to the Pope and his staff.

The oath was administered in the Hall of Blessings in the presence of the Camerlengo Cardinal Eduardo Martínez Somalo and two masters of ceremonies.

On 18 April, the cardinals assembled in St. Peter's Basilica in the morning to concelebrate the mass Pro Eligendo Romano Pontifice (For the Election of the Roman Pontiff).

Archbishop Piero Marini (the Papal Master of Ceremonies) intoned the words extra omnes (Latin, "everybody out!

[22] That source gives the results of the first ballot as:[23] At 20:05 local time, a thin white plume of smoke seemed for a moment to indicate the election was already over, and the 40,000 people who had spent the afternoon watching the ceremonies on large screens in St. Peter's Square broke into applause and song.

"[26] By this point, Cardinal Ratzinger had emerged as a strong contender for the papacy, and recounted in an April 2005 audience to German pilgrims that he felt as though he was beneath the metaphorical axe of papal election, and his head began to spin.

[29] As the voting slips and notes were burnt after that ballot, "All of a sudden, the whole Sistine Chapel was filled with smoke", according to Adrianus Johannes Simonis.