Paul VI

John XXIII convened the Second Vatican Council in 1962 but died in June 1963 before its work was complete, leaving his successor to decide whether to continue, redirect, or quietly close a council whose scope and direction were still being contested even among the bishops attending it. Paul VI, elected weeks later, chose to continue it without significant change of course, presiding over its remaining three sessions through 1965 and signing every one of its sixteen final documents, on subjects ranging from the liturgy and the nature of the church to religious freedom and relations with non-Christian religions.

Implementing those documents fell to Paul VI alone, since the council itself had no ongoing authority once it closed. He authorized the wholesale revision of the Roman Mass into the form promulgated in 1969 and generally called the Novus Ordo, permitting the vernacular language of each country in place of Latin as the ordinary language of the liturgy, a change more visible to ordinary Catholics in daily practice than almost anything else the council produced, and one that provoked lasting resistance among Catholics attached to the older Latin rite.

Paul VI also broke sharply with centuries of papal custom by traveling abroad, becoming the first pope in the modern era to leave Italy repeatedly, visiting the Holy Land in 1964, addressing the United Nations in New York in 1965, and eventually reaching six continents, a pattern of international travel his successors, especially John Paul II, would expand into a defining feature of the modern papacy.

By the mid 1960s, the widespread availability of the contraceptive pill had made the question of artificial birth control urgent for millions of Catholic couples, and Paul VI had appointed a commission of theologians, doctors, and laypeople to study the question, whose majority report was widely understood to lean toward permitting some form of artificial contraception within marriage. Paul VI set the majority recommendation aside and, in the 1968 encyclical Humanae Vitae, reaffirmed the church's traditional teaching that each marital act must remain open to the possibility of life, ruling out artificial contraception while approving natural methods of family planning based on periodic abstinence.

The reaction was immediate and, in parts of the Catholic world, unusually open. Theologians in several countries publicly dissented, some episcopal conferences issued statements softening how the teaching should be applied in pastoral practice, and surveys in the following years showed large numbers of practicing Catholics in Europe and North America not following the encyclical's teaching in their own lives, a gap between official doctrine and lay practice that has persisted for more than fifty years and that later popes have addressed with varying degrees of emphasis without reversing the core teaching.

Paul VI himself is said to have been shaken by the scale and openness of the dissent, and he issued no further encyclical in the remaining decade of his pontificate, a silence some historians read as caution after the reception Humanae Vitae received. He was canonized a saint by Pope Francis in October 2018, fifty years after the encyclical's publication.