The term Catholicism, derived from the Greek adjective καθολικός (katholikos), meaning "general" or "universal", is widely understood to refer to the Church, governed by the Bishop of Rome and the bishops in communion with him. However, other Churches that trace their historic episcopate to the apostolic succession — such as the Oriental Orthodox Churches, the Eastern Orthodox Churches, the Assyrian Church of the East, the Churches of the Anglican Communion, and the Old-Catholics — consider themselves to be branches of the Catholic Church. Neo-Lutheranism argues that Lutheran Churches are simply a Protestant reform movement that remains within the greater Church catholic.

"In the Catholic Church, there are many other things which most justly keep me in her bosom. The consent of peoples and nations keeps me in the Church; so does her authority, inaugurated by miracles, nourished by hope, enlarged by love, established by age. The succession of priests keeps me, beginning from the very seat of the Apostle Peter, to whom the Lord, after His resurrection, gave it in charge to feed His sheep (Jn 21:15-19), down to the present episcopate. "And so, lastly, does the very name of Catholic, which, not without reason, amid so many heresies, the Church has thus retained; so that, though all heretics wish to be called Catholics, yet when a stranger asks where the Catholic Church meets, no heretic will venture to point to his own chapel or house.
"Such then in number and importance are the precious ties belonging to the Christian name which keep a believer in the Catholic Church, as it is right they should .. With you, where there is none of these things to attract or keep me.. No one shall move me from the faith which binds my mind with ties so many and so strong to the Christian religion.. For my part, I should not believe the gospel except as moved by the authority of the Catholic Church." — St. Augustine (354–430): Against the Epistle of Manichaeus called Fundamental, chapter 4: Proofs of the Catholic Faith

A contemporary of Augustine, St. Vincent of Lerins, wrote in 434 under the pseudonym Peregrinus a work known as the Commonitoria ("Memoranda"). While insisting that, like the human body, Church doctrine develops while truly keeping its identity (sections 54-59, chapter XXIII), he stated: "[I]n the Catholic Church itself, all possible care must be taken, that we hold that faith which has been believed everywhere, always, by all. For that is truly and in the strictest sense 'Catholic,' which, as the name itself and the reason of the thing declare, comprehends all universally. This rule we shall observe if we follow universality, antiquity, consent. We shall follow universality if we confess that one faith to be true, which the whole Church throughout the world confesses; antiquity, if we in no wise depart from those interpretations which it is manifest were notoriously held by our holy ancestors and fathers; consent, in like manner, if in antiquity itself we adhere to the consentient definitions and determinations of all, or at the least of almost all priests and doctors" (section 6, end of chapter II).

Many Christians (and denominations) see themselves as "catholic". They fall into two groups:

1) those like the Roman Catholic, Eastern Orthodox, Oriental Orthodox, and Anglican Churches having Apostolic Succession from the early Church; and
2) those who claim to be spiritual descendants of the Apostles but have no discernable institutional descent from the historic Church, and normally do not refer to themselves as catholic.

Of those in the first category, some see their Church as the Catholic Church, others see their Church as only part of the Catholic Church.

For Protestants, most of whom consider themselves to be spiritual descendants (category 2, above), this affirmation refers to their belief in the ultimate unity of all Churches under one God and one Saviour, rather than in one visibly unified institutional Church (category 1, above). In this usage catholic is sometimes written with a lower-case "c". The Western Apostles' Creed, stating "I believe in..the holy catholic church.." (sometimes capitalised), is thus recited in Protestant worship services (with the notable exception of German Lutherans, who substitute "Christian" for "catholic"). The Nicene Creed likewise declares belief in "one, holy, catholic and apostolic Church". It should be noted historically, however, that apostolicity in the form of tactile succession as well as spiritual descent has been maintained by certain national Lutheran Churches (now part of the Porvoo Communion), and has been restored in this fully visible form to the Evangelical Lutheran Church in Canada and the Evangelical Lutheran Church in America through the procedures of full communion agreements with their national Anglican counterparts.

The early Catholic Church came to be organized under the three patriarchs of Rome, Alexandria and Antioch, to which later were added the patriarchs of Constantinople and Jerusalem. The Bishop of Rome was at that time recognized as first among them, as is stated, for instance, in canon 3 of the First Council of Constantinople (381) - many interpret "first" as meaning here first among equals - and doctrinal or procedural disputes were oftentimes referred to Rome, as when, on appeal by St Athanasius against the decision of the Council of Tyre (335), Pope Julius I, who spoke of such appeals as customary, annulled the action of that council and restored Athanasius and Marcellus of Ancyra to their sees. The Bishop of Rome was also considered to have the right to convene ecumenical councils. When the Imperial capital moved to Constantinople, Rome's influence was sometimes challenged. Nonetheless, Rome claimed special authority because of its connection to Saint Peter and Saint Paul, who, all agreed, were martyred and buried in Rome, and because the bishop of Rome saw himself the direct successor of Saint Peter.

The 431 Council of Ephesus, the Third Ecumenical Council, was chiefly concerned with Nestorianism, which emphasized the distinction between the humanity and divinity of Jesus and taught that, in giving birth to Jesus Christ, the Virgin Mary could not be spoken of as giving birth to God. This Council rejected Nestorianism and affirmed that, as humanity and divinity are inseparable in the one person of Jesus Christ, his mother, the Virgin Mary, is thus Theotokos, God-bearer, Mother of God. The first great rupture in the Church followed this Council. Those who refused to accept the Council's ruling were largely Persian and are represented today by the Assyrian Church of the East and related Churches, which, however, do not now hold a "Nestorian" theology. They are often called Ancient Oriental Churches.

The next major break was after the Council of Chalcedon (451). This Council repudiated Eutychian Monophysitism which stated that the divine nature completely subsumed the human nature in Christ. This Council declared that Christ, though one person, exhibited two natures "without confusion, without change, without division, without separation" and thus is both fully God and fully human. The Alexandrian Church rejected the terms adopted by this Council, and the Christian Churches that follow the tradition of non-acceptance of the Council - they are not Monophysite in doctrine - are referred to as Pre-Chalcedonian or Oriental Orthodox Churches.

The next great rift within Christianity was in the 11th century. Doctrinal disputes, as well as conflicts between methods of Church government, and the evolution of separate rites and practices, precipitated a split in 1054 that divided the Church, this time between a "West" and an "East". England, France, the Holy Roman Empire, Scandinavia, and Western Europe in general were in the Western camp, and Greece, Romania, Russia and many of other Slavic lands, Anatolia, and the Christians in Syria and Egypt who accepted the Council of Chalcedon made up the Eastern camp. This division is called the East-West Schism.

The fourth major division in the Church occurred in the 16th century with the Protestant Reformation, after which many parts of the Western Church either entirely rejected the teachings of the Roman Catholic Church and became known as "Reformed" or "Protestant", or else repudiated Roman papal authority and accepted decisions by the civil ruler in religious matters.

A much less extensive rupture occurred when, after the Roman Catholic Church's First Vatican Council, in which it officially proclaimed the dogma of papal infallibility, clusters of Catholics in the Netherlands and in German-speaking countries formed the Old-Catholic (Altkatholische) Church and other Independent Catholic Churches.

All of the preceding groups, excluding some Protestants, consider themselves fully and completely Catholic, either as part of the Catholic Church or as the one and only Catholic Church.

"The Catholic Church", when used not of an abstract invisible entity, but of a visible concrete body of Christians, usually refers to what is also called "the Roman Catholic Church".

This Church does not often use the name "Roman Catholic Church" for itself, except in its relations with other Christian groups. Even in those relations, "Catholic Church" may also appear, as in some documents drawn up in common with the Lutheran World Federation and the Assyrian Church of the East. On the other hand, the Church has in fact applied the adjective "Roman" to itself in its entirety even in some internal documents, such as the Dogmatic Constitution de fide catholica of the First Vatican Council, which was attended by Eastern as well as Western bishops. When it does apply the adjective "Roman" to itself, it understands this word only as pointing to the centrality for it of the see of Rome, with which all its members, laity and clergy alike, are necessarily in full communion. Outsiders, in contrast, considering the use of the name "Catholic Church" by this Church to be contentious, use the term "Roman Catholic Church" to imply that it is only the "Roman" section of some larger, perhaps abstract, entity that they call the Catholic Church and that, in their view, also includes other sections not in communion with Rome, a usage that members of the Church in question in turn see as contentious.

Frequently enough, some members of this Church, especially those of Eastern Rite, apply the term "Roman Catholic Church" not, as in the Church's official documents, to the Church as a whole, but only to its Latin Rite component. Unlike the outsiders just mentioned, these consider communion with the see of Rome essential for all members of the Catholic Church.

In Western Christianity the principal groups that regard themselves as "Catholic" without full communion with the Pope are the Chinese Patriotic Catholic Association and some elements of Anglicanism ("High Church Anglicans" or "Anglo-Catholics"). Smaller groups include the Old Catholics, the Aglipayans (Philippine Independent Church), and the Polish National Catholic Church of America. Their spiritual beliefs and practices are similar to those of Catholics of the Latin Rite, from which they emerged, but they reject the Pope's claimed status and authority.

The Anglican Communion is in practice divided into two wings of unequal size, "High Church Anglicans", also called the Anglo-Catholics, said to be the great majority in most Anglican/Episcopal Churches, and "Low Church Anglicans", also known as the Evangelical wing. Though all elements within the Anglican Communion recite the same creeds, Low Church Anglicans regard the word Catholic in the ideal sense given above, while High Church Anglicans treat it as a name of an identifiable Church which they consider to embrace themselves together with the Catholic, Old-Catholic, and several Eastern Churches.

Anglo-Catholicism has no official fixed tenets, other than rejection of Roman "Ultramontanism," but maintains similarities to both Roman Catholicism and Eastern/Oriental Orthodoxy, as well as to related spirituality, including a belief in seven sacraments, devotion to the Virgin Mary and saints, and emphasize the description of their ordained clergy as "priests", addressed as "Father"(or, in the case of women priests, "Mother"). They have re-emphasized the wearing of vestments and the use of candles and incense and other ceremonial elements in church liturgy, sometimes describing their Eucharistic celebrations with the Latin-derived word "Mass". Some Anglo-Catholics believe in Transubstantiation, as opposed to Consubstantiation, or in other ideas of metousiosis or Real Presence. The development of the Anglo-Catholic wing as a distinct party occurred largely in the nineteenth century, and is strongly associated with the Oxford Movement. Two of its leading lights, John Henry Newman and Henry Edward Manning, both ordained Anglican priests, ended up joining the Catholic Church, becoming cardinals. The parallel "party" among Lutherans, High Church Lutheranism, developed a movement known as Neo-Lutheranism.

The Eastern Orthodox and Oriental Orthodox Churches, as well as the Assyrian Church of the East, each consider themselves to be the universal and true Catholic Church. In various permutations, these bodies typically regard other and Western Catholics as heretical and as having thus left the One, Holy, Catholic, and Apostolic Church. The patriarchs of these Eastern Orthodox and Oriental Orthodox Churches are autocephalous hierarchs, which roughly means that each is independent of the direct oversight of another bishop, although still subject, according to their distinct traditions, either to the synod of bishops of each one’s jurisdiction, or only to a common decision of the patriarchs of their own communion. They are willing to concede a primacy of honor to the Roman See, but not of authority, nor do they accept its claim to universal and immediate jurisdiction. This is similar to the position taken by the Lutheran World Federation, the Anglican Communion, and the Old Catholic Church.