How does the voting work?

The cardinals attended Mass at St. Peter’s Basilica on Wednesday morning, their last public event before being sequestered inside the Vatican, without phone or internet access, until they reach a decision. Inside the Sistine Chapel, they were to take an oath to follow the conclave’s rules, which include maintaining total secrecy.

An initial vote was expected on Wednesday, though the cardinals were unlikely to reach the required two-thirds majority to choose a pontiff.

The papal election is one of the world’s oldest dramas, but this one is unlike any before it, with many cardinals appointed by Francis meeting one another for the first time. The new faces bring unfamiliar politics, priorities and concerns that some experts say could make the conclave more fragmented than usual. Francis also left the church deeply divided, with progressive factions pushing for more inclusion and change and conservatives seeking to roll things back, often under the guise of preserving unity.

Here’s what to know:

• How it works: If, as expected, the cardinals don’t make their pick on Wednesday, they will spend the night at Vatican guesthouses and return to the Sistine Chapel on Thursday. They will participate in four rounds of voting every day until a two-thirds majority agrees on a candidate. There is no indication of how long it will take, though the last two conclaves reached decisions within two days.

• Possible successors: Predicting the outcome of a papal election is always challenging, but oddsmakers say that two top contenders are Cardinal Pietro Parolin of Italy, who was Francis’ second-in-command, and Cardinal Luis Antonio Tagle of the Philippines, a country where the church is growing rapidly.

• Referendum on Francis: The election in many ways will turn on whether the cardinals want a pope who will follow Francis’ path of openness and inclusion or forge a new one. During his 12-year pontificate, Francis made global headlines for landmark declarations that encouraged liberals, including allowing the blessing of people in same-sex unions and raising his voice for migrants.

• Test your knowledge: How well do you know the process of selecting a pope? Take our conclave quiz.

A sea gull sitting on the chimney means … wait, what now?

During the last conclave in 2013, as millions focused their gaze on the roof of the Sistine Chapel, a sea gull landed on the chimney’s metal cover at an opportune moment.

Was it a symbol? A blessing? A sign? Would the white bird signify white smoke?

“That seagull on the Sistine Chapel roof by the conclave is great product placement for the Holy Spirit,” James Martin, a Jesuit priest, posted on Twitter at the time.

The sea gull quickly became the most famous bird in the world. A social media account aptly named the Sistine Seagull was created almost immediately.

“I can see them voting from up here, btw,” the account posted on Twitter, using an abbreviation for “by the way.” “Anybody has any questions, just ask.”

The sea gull remained on the chimney for about 40 minutes.

About an hour after the bird flew away, white smoke emerged from the chimney. Pope Francis had been chosen.

The Sistine Chapel is named after Sixtus IV, who became pope in 1471 and commissioned its construction as the primary chapel of the papal court. It has been posited, though there are skeptics, that the chapel’s dimensions — 131 feet by 42 feet, with ceilings 65 feet high — were meant to recall the Temple of Solomon in Jerusalem as described in the Old Testament, Ms. Jatta said.

Between 1481 and 1483, Sixtus hired some of the greatest artists of the time — Perugino, Botticelli, Signorelli and Ghirlandaio — to fresco the walls of the chapel, which Ms. Jatta said is “symbolic of our faith, our art and our history.” The frescos depict scenes from the lives of Jesus Christ and Moses.

When Julius II, the nephew of Pope Sixtus IV, became pope in 1503, he began an ambitious building program that included revamping St. Peter’s Basilica and completing the Sistine Chapel.

In 1508, he brought in Michelangelo to paint the Sistine’s vault, replacing a previous fresco depicting a starry sky. Working alone on a platform and craning his neck while standing, as a sketched self-portrait shows, Michelangelo painted nine scenes from the Old Testament’s Book of Genesis, and nude figures (known as ignudi), prophets and sybils. It took him four years.

Michelangelo later received a commission from Pope Clement VII to paint the wall behind the altar with a rendering of the Last Judgment. In his biography of Michelangelo, Giorgio Vasari wrote that Clement VII had wanted him to paint the work “so that he could demonstrate in this scene all that the art of design was capable of achieving.”

Michelangelo hadn’t been thrilled by the gig. He considered himself a sculptor first and foremost, “but the pope called him and he was a faithful person,” said Ralf van Bühren, who teaches art history at the Santa Croce Pontifical University in Rome. In “The Last Judgment,” Michelangelo depicted a self-portrait in the skin of flayed St. Bartholomew, to show “he suffered so much, he didn’t like to paint,” he said.

Not everyone was enthusiastic about “The Last Judgment,” with some clerics complaining that too many figures were nude. But Paul III, who became pope in 1534, was a fan. It is said that he fell on his knees, his eyes filling with tears, when the fresco was unveiled in 1541.

Some believe the art will serve as inspiration to the cardinal electors as they gather beneath the frescoes.

“The contemplation of these images evokes the spiritual responsibility of their vote,” Ms. Jatta said.

For the conclave, carpenters built a raised, beige-carpeted platform about two feet above the original floor so that it will be level with the second step leading to the altar. Running the length of the chapel are long tables where the cardinals will sit on cherry wood chairs marked with their names.

The Sistine Chapel has been temporarily closed for days, disappointing tourists who may have planned to visit before Pope Francis’ death on April 21 set the succession process in motion.

Last year, about 7 million visitors trooped through the Sistine Chapel, Ms. Jatta said. The chapel is “hyper monitored” with sensors, she said, and equipped with special lighting and an energy efficient air-conditioning system to minimize wear and tear on the space.

• Scrutineers: Three cardinals who oversee the entire process.

• Infirmarii: Three cardinals who collect the votes of any electors who are sick (though none was believed to be ill as of Wednesday).

• Revisers: Three cardinals who double-check the ballots at the end of each round of voting.

The cardinals, sitting at long tables inside the Sistine Chapel, each receive rectangular pieces of paper printed with the Latin phrase “Eligo in Summum Pontificem,” or, “I elect as the supreme pontiff.” Beneath that, they write the name of their choice for pope.

The 1996 conclave rules specify that the vote must be secret and the candidate’s name legible, “taking care not to write other names as well, since this would make the ballot null.”

One by one, the cardinals walk with their ballot toward the chapel’s altar. Facing the eastern wall, which is decorated with Michelangelo’s “The Last Judgment,” each cardinal utters an oath, in Latin: “I call as my witness Christ the Lord who will be my judge, that my vote is given to the one who before God I think should be elected.”

Then the cardinal places the ballot on a plate and slides it into an urn, traditionally a large chalice.

After all the cardinals have voted, one of the scrutineers mixes the ballots by shaking the chalice. Then the votes are counted individually and placed into a second container. The number of ballots and voters have to match; otherwise, the vote is void.

The ballots are then opened and read by all three scrutineers. The third one announces the name out loud, and records it.

Once the votes have been tallied, a scrutineer pierces each ballot with a needle and threads them together with a red string. After the revisers check the count, the ballots are burned.

Except for the first day, when there is only one vote, two votes take place every morning and two every afternoon, until two-thirds of the cardinals agree on the choice.

I heard a couple of whoops and some applause in the crowd at St. Peter’s Square when Cardinal Pizzaballa took his oath.

The cardinals also vow that the proceedings — including the voting — will remain secret, unless the new pope says that they can break that vow. Any notes taken during the conclave are supposed to be burned with the paper ballots, which are incinerated up to twice a day.

That said, accounts of the secretive deliberations have sometimes trickled out after the election, and some Vaticanisti, as the Vatican press corps is known, have puzzled together about how some choices may have been made. There have also been cases of “secret diaries” by anonymous cardinals that later became public, as in the case of one recounting the election of Benedict XVI in 2005.

The cardinals also pledge not to be swayed by external influences.

Each cardinal then takes an oath in Latin, placing his hand on the Bible and says, “And I,” stating his name, “do so promise, pledge and swear. So help me God and these Holy Gospels which I touch with my hand.”

Once the last cardinal has taken the oath, Diego Ravelli, the master of papal liturgical celebrations will give the order, “extra omnes,” Latin for “everybody out.” He is one of the few people who gets to stay inside the chapel during the conclave, but not while votes are counted.

• Cardinal Blase J. Cupich of Chicago, 76. Born in Nebraska, he was a bishop in South Dakota and an archbishop in Spokane, Wash. His appointment to Chicago in 2014 was one of Pope Francis’ early moves to reshape U.S. church leadership, particularly to show support for immigrants. Cardinal Cupich’s archdiocese covers about two million Catholics in Cook and Lake Counties.

• Cardinal Robert W. McElroy of Washington, 71. The former bishop of San Diego is known for regularly speaking out on behalf of migrants, women and L.G.B.T.Q. people in the church and the United States. He has said that the Trump administration’s plans for a “wider, indiscriminate, massive deportation across the country” would be “incompatible with Catholic doctrine.”

• Cardinal Joseph W. Tobin of Newark, 73. Before coming to Newark, he led the archdiocese of Indianapolis (where he bench-pressed 225 pounds at the gym). As a young priest, he ministered to people with AIDS in Chicago. He has said that he does not see “a compelling theological reason why the pope couldn’t name a woman cardinal.”

• Cardinal Wilton D. Gregory, archbishop emeritus of Washington, 77. The first African-American cardinal, he was president of the United States Catholic bishops’ conference in 2002 and pushed to pass the Dallas Charter, which instituted a zero-tolerance policy for sexual abuse of minors. Later the archbishop of Atlanta, he supported L.G.B.T.Q. Catholics and commissioned an action plan after Francis’ encyclical on the environment.

• Cardinal Kevin J. Farrell, prefect of the Dicastery for the Laity, the Family and Life, 77. The Irish-American was formerly bishop of Dallas. Pope Francis made him the camerlengo, or chamberlain, the Vatican’s acting administrator when a pope dies or resigns. He was responsible for verifying Pope Francis’ death.

• Cardinal Robert F. Prevost, prefect of the Dicastery for Bishops, 69. A Chicago-born priest, he advised the pope on bishop appointments around the world. He is also a member of the Order of Saint Augustine, a religious order of men and women who follow the teachings of the fourth-century saint. Cardinal Prevost is also seen by some as a contender for pope, though a long shot. (There has never been an American pontiff.)

Four other cardinals were elevated by Pope Benedict XVI. They also participated in the 2013 conclave that elected Pope Francis:

• Cardinal Daniel N. DiNardo, archbishop emeritus of Galveston-Houston, 75. He led the archdiocese of 1.7 million Catholics for 19 years, until Pope Francis accepted his resignation in January. He spoke out against separating children from their parents at the border during President Trump’s first term, calling it “immoral.” He is also a former president of the United States Catholic bishops’ conference.

• Cardinal Timothy M. Dolan of New York, 75. The leader of New York’s 2.5 million Catholics since 2009, he was previously the archbishop of Milwaukee and rector of the Pontifical North American College, a seminary in Rome. He is a favorite of center-right Catholics on issues like abortion, and fought the Obama administration’s rule requiring some religious groups to provide contraception for employees. He led prayers at both of President Trump’s inaugurations.

• Cardinal James M. Harvey, archpriest of the Basilica of St. Paul Outside the Walls, 75. Born in Milwaukee, he has spent decades in roles at the Vatican, including being in charge of the papal household under Popes John Paul II and Benedict XVI. The Basilica where he presides in Rome is where many believe St. Paul is buried.

• Cardinal Raymond L. Burke, patron of the Order of Malta, 76. A canon law scholar, he has become a conservative celebrity, the de facto leader of the opposition to Pope Francis’ agenda and a traditionalist with an affinity for the Latin Mass. The pope had removed him from leadership positions. “I’m called the enemy of the pope, which I am not,” Cardinal Burke said in 2019.

Prediction markets correctly forecast President Trump’s victory in November, but picking the next heir to St. Peter’s throne is likely to be a tougher challenge, experts on both the Vatican — known as the “vaticanisti” — and elections say.

The wisdom of crowds can go only so far. High-tech betting sites “will never be able to break through the complexity, the unpredictability of the decisions made inside,” said Franca Giansoldati, a Vatican specialist who writes for Il Messaggero, one of Italy’s biggest daily newspapers.

Rajiv Sethi, an economist at Barnard College who has studied prediction markets, noted that when it came to the presidential election, bettors were able to process a wide variety of information sources, including public polls and televised debates. The papal conclave — famously conducted behind closed doors and composed of an expected 133 cardinal electors sworn to secrecy — offers far fewer clues for gamblers.

“We can rule out information leakage from cardinals,” Mr. Sethi said.

Conclave politics have been highly unpredictable. In 2013, the favorite was Cardinal Angelo Scola; Cardinal Jorge Mario Bergoglio, who became Pope Francis, was on few short lists. (That’s a reminder that, as Vaticanisti often say: Whoever enters the conclave as pope exits a cardinal.)

This time the cardinals again appear divided, and many are meeting for the first time, factors that could complicate how long it takes before white smoke emerges from the Sistine Chapel. Once the cardinals are locked inside, their politicking and alliance-building are obscured.

Conclaves often turn on moments out of public view, when “everything can turn upside down in an instant,” said Stefano Maria Paci, a vaticanista for L’Espresso, one of Italy’s most-read weekly newsmagazines.

“I am convinced this is the hardest vote on the planet to forecast,” he added.

That is unlikely to deter online bettors. By Wednesday afternoon, the Kalshi and Polymarket wagers on the outcome of the conclave had exceeded $27 million. By comparison, the Super Bowl drew $27 million in bets on Kalshi alone.

“I do,” said Cardinal Dolan, “because in the conclave is mostly silence.”

When the cardinals meet for the conclave, they gather in the Sistine Chapel. All cardinal electors must swear an oath of secrecy and vote by secret ballot. The cardinals cast repeated votes until there is a two-thirds majority, and the next pope is selected.

The voting process can take an hour or two each time, so there is a lot of waiting while each cardinal fills out his ballot and submits it in an elaborate ritual to ensure there are no election violations, he said.

“It’s not like you’re at the edge of the seat, and watching them all do that,” said Cardinal Dolan, who attended the conclave that elected Pope Francis in 2013.

He’s bringing a biography of Michelangelo, which felt appropriate, as he will be surrounded by some of the artist’s masterpieces, including “The Last Judgment,” which depicts the second coming of Christ and covers the altar wall of the Sistine Chapel.

Cardinal Dolan said he had top candidates for pontiff in mind, men whose writing and work he has studied.

“You want to see a guy who speaks well, you look for some linguistic ability. It would be very difficult for someone who did not know enough Italian,” he said. “If you don’t know the difference between carbonara and tagliatelle, you’re in trouble. It would be very difficult for somebody who only knows Italian, because you’re also a universal pastor.”

As he spoke, he looked down at St. Peter’s Basilica from the roof terrace of the Pontifical North American College.

“I think it’ll be longer than last time,” he said, referring to the process that selected Pope Francis, which took two days. He said he had brought 12 packets of peanut butter, thinking that would be enough for him to eat three a day while sequestered. “So you figure that out,” he said on the math.

The meetings held before the conclave have been “strenuous,” he said, with “one cardinal after another” getting up to speak.

Cardinal Dolan said the cardinals had shared their concerns about what they see as challenges for Christians in Islamic countries; in countries with oppressive governments; in regions without enough Catholic priests; or where religious liberty is suppressed.

“Think of the cardinal from Sudan. Think of the cardinals from the Holy Land,” he said.

One cardinal was grateful that Francis had traveled all over the world, he said, while another said maybe the next pope should largely stay at the Vatican and bring cardinals to meet with him there.

“One of the cardinals said, I love Pope Francis, and I am grateful for his 12 years. But we are here to elect the successor of Peter, not the successor of Francis,” he said, referring to St. Peter, the first pope. “That of course is true.
We have to remember that.”

The ancient and elaborate rituals of the conclave can be mystifying for those watching from afar. But new cardinals “will also say, we don’t really know the rituals and the protocol, we don’t even know what to wear,” he said. “They’re so honest and they’re so fresh.”

After a morning Mass on Wednesday, the cardinals are expected to go back to Casa Santa Marta, unpack and have lunch. The accommodation and cuisine are relatively simple. “The food’s not that good,” Cardinal Dolan said.

The process is also extremely secretive, so much so that at the last conclave, even the blinds of Cardinal Dolan’s windows were secured shut so that no one could see in or out.

Vatican City shuts down, and the cardinals are sequestered, but they have a physician and a confessor available, “if we need help in body or soul,” he said.

Giovanni Battista Re, the spry, 91-year-old dean of the College of Cardinals, presided over the Mass in the basilica built on the tomb of St. Peter, the Roman Catholic Church’s first pope. In his homily, Cardinal Re made a pitch to his peers to elect a pope “whom the church and humanity need at this difficult, complex and tormented turning point in history.”

He also implored the voting cardinals to choose “a pope who knows how best to awaken the consciences of all, and the moral and spiritual energies in today’s society.” (Those words could offer a boost to more charismatic candidates.)

The homily was not transparently political, but it also included some strong messages to the cardinals, such as a plea “to maintain the unity of the church.” Some liberals have worried that conservatives are campaigning to roll back Pope Francis’ agenda of inclusion under the guise of preserving unity. Cardinal Re added that Christ wanted “a unity that does not mean uniformity, but a firm and profound communion in diversity.”

Cardinal Re cannot vote in the conclave because he is over 80, the cutoff age. He is nevertheless a veteran of conclaves and knows what it is like inside the Sistine Chapel during the election. In the homily, he talked about selflessness and Judas, the apostle who betrayed Christ, and urged the cardinals to set aside “personal considerations” as they make their decision.

Quoting Pope John Paul II, Cardinal Re expressed hopes that Michelangelo’s painting of Jesus as the judge in the Sistine Chapel would “remind everyone of the great responsibility” of placing the papacy “in the correct hands.”

Wearing bishop’s miters and red capes with golden embroidery, the cardinals proceeded over the marble floor of St. Peter’s central aisle as an organ played and Latin chants resounded in the basilica. An attendant asked the worshipers not to clap as the prelates entered.

One playfully tapped another on the cheek. Several held canes.

Cardinal Matteo Zuppi of Italy, who has emerged as a leading contender for pope — and who appeared to have a fresh haircut — warmly shook his peers’ hands.

After Mass, the cardinals removed their capes and headed for lunch at Casa Santa Marta, the guesthouse where they will be staying until they elect a pope. Some carried tote bags.

Cardinal Jean-Marc Aveline of France, who has also been mentioned as a papal contender, stopped for a prayer in front of the reliquary containing the remains of Pope John XXIII — a hero to many liberal Catholics for his efforts to modernize the church.