Benedict XVI, in the Apostolic Letter "Normas nonnullas," established with minimal modifications the procedure for the election of the Supreme Pontiff, detailing all the steps to be taken from the Pope's death to the election of the new one.
According to this text, a maximum of 120 cardinals will be the electors of the new Pontiff. All of them must be under 80 years of age on the day the Apostolic See becomes vacant. Throughout the election period, the electors' rooms will be located in the Vatican City State - at the Casa Santa Marta - to ensure isolation within its walls. Given the "sacred nature of the act," the election will take place in the Sistine Chapel, "where everything contributes to making the presence of God more vivid." Everything related to the election operations must be carried out in the "strictest secrecy."
During the vacant see, two types of congregations of the cardinals will take place: a general one, with the entire College until the start of the election, and a particular one. The latter is composed of the Camerlengo cardinal and three cardinals, one from each order, drawn by lot from the elector cardinals who have arrived in Rome. "The cardinals must wear the ordinary black cassock with a red cord and red sash, with a skullcap, pectoral cross, and ring."
In one of the congregations immediately after the Pope's death, the day, time, and manner in which the deceased Pontiff's body will be transferred to St. Peter's Basilica to be exposed for veneration will be established. The funeral rites will last for nine days. The congregation will set the start of the rites so that the burial takes place between the fourth and sixth day after death. It will also be responsible for destroying the Fisherman's Ring and the lead seal, as well as assigning the elector cardinals' rooms by lot and setting the day and time for the start of the voting operations.
Upon receiving the news of the Pope's death, the Camerlengo must officially verify the death, and the Chancellor of the Apostolic Chamber must draw up the official death certificate or document. The study and the Pontiff's room will be sealed, and everything related to the Pope's burial will be arranged.
After the Pontiff's death, the cardinals will celebrate funeral rites for his soul for nine consecutive days. No one is allowed to take any images of the sick or deceased Supreme Pontiff by any means, nor record his words in his agony with any instrument for later reproduction. If someone wants to take photographs for documentation after the Pope's death, they must request permission from the Camerlengo cardinal, but it will not be allowed under any circumstances if the Pope is not dressed in pontifical attire.
After the burial and during the election of the new Pope, no part of the private apartment he occupied may be inhabited. After the death, 15 complete days will be waited to allow the cardinals time to arrive in Rome before the Conclave begins. However, the College of Cardinals may advance the start of the Conclave if all electors are present, or delay it for serious reasons. Nevertheless, the period for the Conclave to begin from the vacant see cannot exceed 20 days.
From the start of the election process until it occurs and is publicly announced, the elector cardinals must refrain from corresponding by letter, telephone, or other means of communication with people outside the election sphere. They may not converse with anyone present in the Vatican City, receive press, listen to radio programs, or watch television broadcasts. During this period, various language-speaking religious individuals will be available for confessions, as well as two doctors and staff for dining and cleaning services. All must swear to maintain "absolute and perpetual secrecy" regarding everything related to the voting and scrutiny of the election.
Once the funeral rites of the deceased Pope have been celebrated, the cardinals will celebrate a "pro eligendo Papa" mass. From there, in "choir attire, in a solemn procession, invoking with the singing of the Veni Creator the assistance of the Holy Spirit," they will proceed to the Sistine Chapel to begin the election process. The chapel will have undergone strict controls to prevent the "fraudulent" installation of audiovisual recording and transmission devices to the outside. If there is any violation of the secrecy rule, the perpetrators will be subject to excommunication.
All cardinals will swear to keep the secret, and the Master of Liturgical Celebrations will pronounce the "extra omnes," after which all outsiders to the Conclave must leave the Sistine Chapel, and the election operations will begin.
For the valid election of the new Pope, at least two-thirds of the votes are required, calculated on the total number of present and voting electors. If the election does not take place on the first day of the Conclave, two votes will be held daily, in the morning and afternoon.
The distributed ballots must be rectangular and must bear the printed phrase, Eligo in Summum Pontificem. Each cardinal will write a single name on it. The ballots are placed in an urn, and each cardinal will say the following formula: "I call as my witness the Lord Christ, who will judge me, that I am voting for the one who, in the presence of God, I believe should be elected."
The scrutiny is done aloud, and as each ballot is read, it is pierced with a needle at the word Eligo and threaded onto a string. The ends of the string are tied with a knot. Then the votes are counted, and if a name has obtained two-thirds of the total, the election is considered valid. Otherwise, the procedure will be repeated twice daily. Elector cardinals are prohibited from making any pact, agreement, or promise that obliges them to vote for a specific name. Violation of this rule implies excommunication.
Once the new Pope is elected and this fact is communicated with the traditional fumata blanca, the chosen one must give his consent: "Do you accept your canonical election as Supreme Pontiff?" And after receiving a yes, he is asked, "How do you wish to be called?" After this ceremony, the chosen one immediately becomes the "Bishop of the Roman Church, the true Pope, and Head of the Episcopal College."