The Chi Rho symbol.
Roman Catholicism, also known simply as Catholicism, is the largest Christian denomination, with 1.3 billion baptized adherents by 2017. Roman Catholicism, derived from the Greek word katholikos ("universal"), is the theological ideology of the Roman Catholic Church (both the Latin and Eastern churches), and its core tenets are derived from the Nicene Creed. Roman Catholicism teaches that the Roman Catholic Church is the "One, Holy, and Apostolic church" founded by Jesus in his Great Commission, that its bishops are the successors of the Twelve Apostles, and that the Bishop of Rome (the Pope) is the successor to Saint Peter upon whom primacy was conferred by Jesus.
In addition to the Nicene Creed, Roman Catholicism's other guiding tenets include the Seven Sacraments: baptism, confirmation, eucharist, penance, anointing of the sick, holy orders, and matrimony, which are meant to guide the lives of adherents of the Catholic faith. Roman Catholics believe in consubstantiation (the priest's consecration of bread and wine as the literal body and blood of Christ), Divine Mercy, sanctification through faith and evangelism, voluntary support for the sick and poor, and the veneration of Mary as Mother of God and Queen of Heaven. Catholicism was once the dominant religion of the Western world, but the Muslim conquest of the Levant and North Africa, the 1054 Great Schism with Orthodox Christianity, the 16th century Protestant Reformation and the split of
Protestantism, and the rise of secularism and atheism in the West from the 19th to 21st centuries led to Catholicism's decline. By the 21st century, the majority of Catholics lived in South America and Africa, and Catholicism declined in the secular West due to support for the separation of Church and state, the Roman Catholic Church's clergy sexual abuse epidemic, and a shortage of priests in the church.