Catholicity (from Ancient Greek: καθολικός, romanized: katholikós, lit. 'general', 'universal', via Latin: catholicus) is a concept pertaining to beliefs and practices that are widely accepted by numerous Christian denominations, most notably by those Christian denominations that describe themselves as catholic in accordance with the Four Marks of the Church, as expressed in the Nicene Creed formulated at the First Council of Constantinople in 381: "[I believe] in one, holy, catholic, and apostolic Church."

The Catholic Church is also known as the Roman Catholic Church; the term Roman Catholic is used especially in ecumenical contexts and in countries where other churches use the term catholic, to distinguish it from broader meanings of the term. Though the community led by the pope in Rome is known as the Catholic Church, the traits of catholicity, and thus the term catholic, are also ascribed to denominations such as the Eastern Orthodox Church, the Oriental Orthodox Church, the Assyrian Church of the East. It also occurs in Lutheranism, Anglicanism, as well as Independent Catholicism and other Christian denominations. While traits used to define catholicity, as well as recognition of these traits in other denominations, vary among these groups, such attributes include formal sacraments, an episcopal polity, apostolic succession, highly structured liturgical worship, and other shared Ecclesiology.

Among Protestant and related traditions, catholic is used in the sense of indicating a self-understanding of the universality of the confession and continuity of faith and practice from Early Christianity, encompassing the "whole company of God's redeemed people". Specifically among Methodist, Lutheran, Moravian, and Reformed denominations the term "catholic" is used in claiming to be "heirs of the apostolic faith". These denominations consider themselves to be part of the catholic (universal) church, teaching that the term "designates the historic, orthodox mainstream of Christianity whose doctrine was defined by the ecumenical councils and creeds" and as such, most Reformers "appealed to this catholic tradition and believed they were in continuity with it." As such, the universality, or catholicity, of the church pertains to the entire body (or assembly) of believers united to Christ.