The Roman Catholic Church, officially known as the Catholic Church, is the world's largest Christian church, representing over half of all Christians and one-sixth of the world's population. The Catholic Church is a communion of the Western Rite (Latin Rite) and 22 autonomous Eastern Catholic Churches (called particular churches), comprising 2,795 dioceses in 2008.

The Church's highest earthly authority in matters of faith, morality and Church governance is the Pope, currently Pope Benedict XVI, who holds supreme authority in the Church in concert with the College of Bishops, of which he is the head. The Catholic community is made up of an ordained ministry and the laity; members of either group may belong to organized religious communities.

The Church defines its mission as spreading the gospel of Jesus Christ, administering the sacraments and exercising charity. It operates social programs and institutions throughout the world, including schools, universities, hospitals, missions and shelters, as well as organizations such as Catholic Relief Services, Caritas Internationalis and Catholic Charities that help the poor, families, the elderly and the sick.

Through apostolic succession, the Church believes itself to be the continuation of the Christian community founded by Jesus in his consecration of Saint Peter, a view shared by some historians. It has defined its doctrines through various ecumenical councils, following the example set by the first Apostles in the Council of Jerusalem. On the basis of promises made by Jesus to his apostles, described in the Gospels, the Church believes that it is guided by the Holy Spirit and so protected from falling into doctrinal error.

Catholic beliefs are based on the deposit of Faith (containing both the Holy Bible and Sacred Tradition) handed down from the time of the Apostles, which are interpreted by the Church's teaching authority. Those beliefs are summarized in the Nicene Creed and formally detailed in the Catechism of the Catholic Church. Formal Catholic worship, termed the liturgy, is regulated by Church authority. The Eucharist, one of seven Church Sacraments and the key part of every Catholic Mass or Eastern Catholic Divine Liturgy, is the center of Catholic worship.

With a history spanning almost two thousand years, the Church is one of the world's oldest institutions and has played a prominent role in the history of Western civilization since at least the 4th century. In the 11th century, a major split (the Great Schism) occurred between Eastern and Western Christianity, largely as a result of disagreements over papal primacy. The Eastern Orthodox churches became a separate entity from the Catholic Church in the resulting schism. Eastern Churches who remained in or later re-established communion with the Bishop of Rome, the Pope, form the Eastern Catholic churches. In the 16th century, partly in response to the Protestant schism, the Church engaged in a substantial process of reform and renewal, known as the Counter-Reformation.

Although the Church maintains that it is the "one, holy, catholic and apostolic Church" founded by Jesus Christ where one can find the fullness of the means of salvation, it also acknowledges that the Holy Spirit can make use of other Christian communities to bring people to salvation. It believes that it is called by the Holy Spirit to work for unity among all Christians, a movement known as ecumenism. Modern challenges facing the Church include the rise of secularism and opposition to its stances on abortion, euthanasia, contraception, and sexual morality.