The next pope will inherit a church facing serious challenges, such as the polarization between liberals and conservatives, competition with evangelical Protestants, the secularization of Western Europe and the clergy's steadily declining ranks.
The new pontiff will have to find a way to bridge the chasm between the message he preaches and the practices of his flock, who often ignored Pope John Paul II's strict teachings on divorce, premarital sex and contraception.
In the United States, he will need to help restore the credibility of the church after the priest sex abuse scandal - the worst in the history of the American church. And globally, the Vatican must manage an increasingly diverse church where the engine of growth, and many say the future, lies in Latin America, Asia and Africa.
One of the main issues for the next pope will be improving relations between the Vatican and the rest of the church.
The Second Vatican Council (1962-1965) emphasized more openness with a "collegial" or power-sharing arrangement between the pope and world's more than 5,000 bishops. During Pope John Paul's pontificate, however, the Vatican centralized decision-making, stripped power from the national bishops' conferences and cracked down on theologians who questioned the pope's stand on controversial issues.
Critics say the result was a top-down bureaucracy that stifled debate on tough questions and lost touch with the reality of Catholic life.
"In some ways, we are at a dead end right now," said the Rev. John Langan, a professor of Catholic social thought at Georgetown University, who was interviewed before the pope's death. "The traditional positions can be repeated and enforced in certain settings, but they pretty well lost the support of large numbers both in the academic and cultural leadership and just ordinary people."
Under Pope John Paul, the Vatican targeted theologians and organizations who strayed from his orthodox line. The approach was markedly tougher than that of his recent predecessors, Pope Paul VI (1963-1978) and Pope John XXIII (1958-1963), perhaps the most beloved pope in history.
Pope John Paul, unhappy with the Jesuits' role in preaching liberation theology and for supporting revolutionary movements in Latin America, suspended the order's constitution in the early 1980s and temporarily put his own man in charge. Cardinal Joseph Ratzinger, the Vatican's enforcer of theology, launched a lengthy investigation of Jacques Dupuis, a widely respected theologian who argued that other religions could offer salvation.
The Vatican also took aim at bishops, declaring that the decisions they made in national conferences were mere opinions carrying no theological weight. The loss of power weakened local leadership in the United States when it was sorely needed, according to Margaret Steinfels, former editor of Commonweal, a lay Catholic magazine.
"I think depriving the conference of the kind of cohesion and authority was a huge mistake," Steinfels said, "and its inability to respond to the sex abuse crisis is the surest sign of that."
Pope John Paul took strong positions against abortion, homosexuality and contraception, winning great support among traditionalists. Theologians who challenged those stands were punished.
The Rev. Charles Curran lost his job teaching moral theology at the Catholic University of America in Washington in the late 1980s for favoring contraception and the remarriage of divorced Catholics. Curran said he was targeted in a campaign designed to encourage self-censorship.
"They were selectively picking out various people in different parts of the world," said Curran, now a theology professor at Southern Methodist University in Dallas. "You got a chilling effect."
Not everyone saw Pope John Paul as an authoritarian. Fellow conservatives point out that the pope met extensively with bishops and listened to their concerns, even if he did not always agree with them.
"Those who complain about [a lack of] collegiality should be asked what do they have in mind?" said Michael Novak, who studies religion, philosophy and public policy at the American Enterprise Institute in Washington. "I think implicitly they want a pope who thinks like them."
Despite public admiration of the pope, much of the flock in the United States and Europe disagreed with Pope John Paul on major issues. According to one study, 70 percent of Catholics in Rome essentially ignored the pope's pronouncements and approved of divorce, birth control, premarital sex and cohabitation.
"The charisma only extended so far," said Chester Gillis, a professor of theology at Georgetown University. "They cheered the pope, they loved the pope and they revered him in his presence. Then they went home and practiced birth control."
Bridging the gap between traditional teaching and liberal practice won't be easy for Pope John Paul's successor. Observers, though, suggest less finger-wagging and more sensitivity to the pressures ordinary Catholics face might produce a more credible message.
"I would like to see much more consultation, a more pastoral style of teaching, not this constant repetition of traditional answers to what are often new questions," said the Rev. Thomas P. Rausch, a professor of theology at Loyola Marymount University in Los Angeles.
Some of those new questions spring from the dizzying pace of biotechnology development, an area in which the church has often struggled to articulate a position. For instance, the Vatican opposes in-vitro fertilization because it is unnatural and involves the eventual destruction of embryos. Catholic theologians, though, have not yet decided whether implanting an embryo from one woman into another violates natural law.
In failing to make swift, clear decisions, the church runs the risk of irrelevance in a world that moves much faster than the Vatican's snail-like bureaucracy.
"Everyone agrees you can't just look this up in the Bible," said Princeton professor Robert P. George, a strong Pope John Paul supporter who sits on President Bush's bioethics council. "It's a difficult problem, and we are going to have to think it through together."
During his 26 years in power, Pope John Paul presided over a shortage of priests as the number of Catholics increased by 40 percent. In the United States, the number of working priests is expected to decline from 23,098 in 1998 to 15,136 in 2010. Much of the growth came in the developing world, where two-thirds of the world's Catholics now live. Most of the priests, though, live in Europe and North America.
The burgeoning faithful in Latin America, Africa and Asia are creating managerial and cultural challenges for the Vatican, which has resisted incorporating local culture into religious practice and insists on approving liturgical translations.
"How many people in Rome know Japanese?" said the Rev. Peter Phan, author of In Our Own Tongues: Perspectives from Asia on Mission and Inculturation. "How many people in Rome know the culture?"
The church faces other challenges abroad, including conflict with Islam in nations such as Nigeria, Sudan and the Philippines.
The government of the heavily Catholic Philippines is battling Muslim guerrillas in the south. In recent years, thousands of Muslims and Christians have died in political, ethnic and religious violence in northern Nigeria, where Muslims have instituted Sharia, or Islamic law.
The shortage of clergy has left the Catholic Church vulnerable to competition from evangelical Protestants in Latin America. And in the United States, many parishes don't have full-time priests.
Analysts attribute much of the priest shortage to the celibacy requirement. David Gibson, author of The Coming Catholic Church, predicts that the next pope or his successor will make it optional.
In some respects, the change is already occurring on the ground, said Gibson. The U.S. Catholic Church has at least 150 married priests. Most of them are former Episcopalians who came to Catholicism with wives and children when they converted.
Clerical celibacy has been a part of the church for centuries, but it is a discipline - not doctrine. St. Peter and many of the apostles had wives. In theory, the pope could lift the requirement of celibacy anytime.
Ordination of women is far less likely. In 1993, Pope John Paul opposed it in an apostolic letter, saying Christ had only chosen men as apostles and therefore only men could be priests. The letter effectively ended debate on the issue, further alienating many Catholic women, who typically pass on the faith to children.
Said the Rev. Thomas Reese, author of Inside the Vatican: "If we lose women in the 21st century, we might as well close shop."