The death of Pope John Paul II set in motion a complicated period of transition, an interval marked by mourning, a slowdown in Vatican operations and the election of a new pope.

Regulated by ancient traditions and recent rules, the period between popes—known by the Latin term “interregnum”—began moments after the pope’s death April 2.

It ends when the College of Cardinals, meeting in a closed-door conclave, chooses a successor and announces it to the world. The start of the conclave has been set for April 18.

The rules governing the interregnum are matters of church law, not dogma, and were last revised by Pope John Paul in 1996, in his apostolic constitution “Universi Dominici Gregis.”

The document confirmed that as long as the Holy See is vacant, the universal church is governed by the College of Cardinals, which cannot, however, make decisions normally reserved to the pope. Such matters must be postponed until the new pope is elected.

And until there is a pope, the Roman Curia—the Vatican’s network of administrative offices—loses most of its cardinal supervisors and cannot handle any new business.

The College of Cardinals is to deal solely with “ordinary business and matters which cannot be postponed.” At present, there are 183 cardinals, and all of them were asked to meet in Rome to help administer the transition period.

The College of Cardinals does this through two structures: a general congregation, in which all the cardinals were to begin meeting daily; and a particular four-member congregation, consisting of the chamberlain of the Holy Roman Church, Cardinal Eduardo Martinez Somalo, and a rotating team of three cardinal assistants.

Only those cardinals under age 80—a total of 117—will be eligible to vote in the coming conclave.

As chamberlain, Cardinal Martinez Somalo is to administer the goods and temporal rights of the Holy See until the election of a new pope. His duties also included verifying the death of the pope, sealing the pope’s private rooms, taking possession of papal palaces at the Vatican and elsewhere, and informing leading churchmen of the pope’s death. He also was to make arrangements for Pope John Paul’s burial, unless the pope left his own instructions in this regard.

The chamberlain also may grant requests to photograph the deceased pope, but only if the pope is wearing pontifical vestments.

Meanwhile, the dean of the College of Cardinals, Cardinal Joseph Ratzinger, had the duty of informing the other cardinals of the pope’s death and convoking them for the first congregations, as well as informing the diplomatic corps and the heads of nations.

The cardinals in charge of major Vatican departments have lost their positions with the death of the pope, although they may be brought back to their jobs by the next pontiff. During the interregnum, most curial offices are to be overseen by the secretaries of each department, who are generally bishops.

Thus the Roman Curia keeps functioning, but at a slower pace. Pope John Paul’s apostolic constitution instructed the Curia to avoid action on “serious or controverted matters,” so that the next pope will have a free hand in dealing with these issues. The Vatican’s tribunals continue to process marriage and other cases, and the Vatican’s diplomatic representatives remain in place.

Among the first items that faced the College of Cardinals were arranging for the pope’s body to be taken to St. Peter’s Basilica for homage by the faithful, setting the time for the funeral rites, which are celebrated for nine consecutive days, reading the pope’s will, and setting the date for the start of the conclave.

In addition, the cardinals must:

– See to it that the Sistine Chapel is prepared for the conclave and the rooms of the Domus Sanctae Marthae are readied for the cardinal-electors who will stay there once the conclave begins. The Domus, an ecclesial guest house completed in 1996 inside Vatican City, will provide spacious and comfortable housing for the cardinals for the first time in centuries.

– Ask two churchmen to present two meditations to the cardinals on problems facing the church and the need for careful discernment in choosing the new pope.

– Read any documents left by the dead pope for the College of Cardinals.

– Arrange for destruction of the papal fisherman’s ring and personal seals.

During this time, the cardinals may discuss the coming election among themselves. However, the cardinals may not make pacts or agreements that would oblige them to vote for a particular candidate. All cardinals take an oath to maintain strict secrecy regarding everything related to the conclave, even after it is over.

The word conclave comes from Latin, meaning literally “with key,” and reflects the previous tradition of locking the cardinals in an area where they would spend day and night until the new pope’s election. This time, although the principle of a closed procedure still holds, the cardinals will be taken by bus from their residence to the Sistine Chapel for voting. They are not to communicate with the outside world, watch TV or read newspapers.

On the day set for entry into the conclave, the cardinal electors assemble in St. Peter’s Basilica to attend morning Mass. In the afternoon, they walk in procession to the Sistine Chapel, located just to the north of St. Peter’s. Rules specify that the chapel is to be swept for listening or recording devices beforehand.

The voting may begin that afternoon with one ballot; on following days, normally two ballots are held in the morning and two in the afternoon. In this stage, a pope is elected when he obtains at least two-thirds of the votes. Pope John Paul abolished a prior form of election by acclamation, which had never been used in modern times.

All voting is secret, in writing, on paper ballots, which are deposited in a receptacle by each elector, then counted. Ballots are taken to any cardinals residing at the Domus Sanctae Marthae but who are too sick to come to the Sistine Chapel.

After each morning and afternoon round of voting, the ballots are burned. By tradition but not by rule, the successful election of a new pope is signaled to the world by white smoke coming out of the Sistine Chapel smokestack—an effect obtained by the addition of chemicals to the burning ballots, but which has led to confusion in the past.

In the first phase of voting, a period of about 12 days, the rules foresee about 30 possible ballots, with occasional pauses for reflection. If, after that phase, the conclave has not elected a new pope, the cardinals discuss whether to proceed to election by simple majority vote. If they do, they can also limit the voting to the top two candidates.

Once a new pope has been elected, he is asked if he accepts the office—he is encouraged but not bound to do so by the current rules—and is asked to choose a name. Since 1404, the new pope has always been a cardinal.

Traditionally, the senior member of the cardinal deacons—currently Cardinal Jorge Medina Estevez, 78—announces the successful election results from the central balcony of St. Peter’s Basilica. After the new pope has donned papal robes, he proceeds to the balcony, where he greets the public and offers his first blessing.

At a time designated by the pope, usually a few days later, he officially opens his ministry with an investiture Mass at St. Peter’s. The new pope is no longer crowned with a papal tiara, but receives a pallium, or stole, in recognition of his authority.