Catholic is an adjective derived from the Greek adjective (katholikos), meaning "whole" or "complete". In the context of Christian ecclesiology, it has a rich history and several usages. For Roman Catholics, the term "Catholic Church" refers to the Church in full communion with the Bishop of Rome, including both the Western particular Church and the Eastern Catholic Churches. Protestants sometimes use the term "catholic church" to refer to the entire body of believers in Jesus Christ across the world, and across the ages. Eastern Orthodox, Anglican, and some Methodist Christians hold that their churches are catholic in the sense that they are in continuity with the original catholic (universal) church founded by the apostles. In "Catholic Christendom" (including the Anglican Communion), bishops are considered the highest order of ministers within the Christian Church, as shepherds of unity in communion with the whole church and one another.  Catholicity is considered one of Four Marks of the Church, the others being unity, sanctity, and apostolicity. according to the Nicene Creed of 381: "I believe in one holy catholic and apostolic Church."
A letter written by Ignatius to Christians in Smyrna around 106 is the earliest surviving witness to the use of the term catholic church (Letter to the Smyrnaeans, 8). By catholic church Ignatius designated the Christian Church in its universal aspect, as "catholic" still meant no more than "universal", since it was only later that the word "catholic" took on the ecclesiastical meaning of "orthodox and apostolic". Ignatius considered that certain heretics of his time, who disavowed that Jesus was a material being who actually suffered and died, saying instead that "he only seemed to suffer" (Smyrnaeans, 2), were not really Christians. The term is also used in the Martyrdom of Polycarp in 155 and in the Muratorian fragment, about 177.
St Cyril of Jerusalem (circa 315-386) urged those he was instructing in the Christian faith: "If ever thou art sojourning in cities, inquire not simply where the Lord's House is (for the other sects of the profane also attempt to call their own dens houses of the Lord), nor merely where the Church is, but where is the catholic church. For this is the peculiar name of this Holy Church, the mother of us all, which is the spouse of our Lord Jesus Christ, the Only-begotten Son of God" (Catechetical Lectures, XVIII, 26).
The term catholic Christians entered Roman Imperial law when Theodosius I, Emperor from 379 to 395, reserved that name for adherents of "that religion which was delivered to the Romans by the divine Apostle Peter, as it has been preserved by faithful tradition and which is now professed by the Pontiff (Pope) Damasus and by Peter, Bishop of Alexandria ...as for the others, since in our judgement they are foolish madmen, we decree that they shall be branded with the ignominious name of heretics, and shall not presume to give their conventicles the name of churches." This law of 27 February 380 was included in Book 16 of the Codex Theodosianus. It established catholic Christianity as the official religion of the Roman Empire.
The use of the term catholic to distinguish the "true" church from heretical groups is found also in Augustine who wrote:
"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).
The Latin Rite of the Roman Catholic Church and the twenty-two Eastern Catholic Churches fully accept this tradition and feel charged with preserving it. Eastern Catholic Churches are autonomous (in Latin, sui iuris) particular Churches in full communion with the Bishop of Rome — the Pope. They preserve the liturgical, theological and devotional traditions of the various Eastern Christian Churches with which they are associated. They include the Ukrainian, Greek, Greek Melkite, Maronite, Ruthenian Byzantine, Coptic Catholic, Syro-Malabar, Syro-Malankara, Chaldean and Ethiopic Rites. Under Pope John Paul II the Catholic Church issued a book of beliefs, common to all these churches under the title Catechism of the Catholic Church, which states: "To believe that the Church is 'holy' and 'catholic,' and that she is 'one' and 'apostolic' (as the Nicene Creed adds), is inseparable from belief in God, the Father, the Son, and the Holy Spirit."
The term Catholic Church is associated with the whole of the church that is led by the Roman Pontiff, currently Pope Benedict XVI, and whose over one billion adherents are about half of the estimated 2.1 billion Christians. Other Christian denominations also lay claim to the description catholic, including the Eastern Orthodox Church and those Churches possessing the historic episcopate (bishops), such as those in the Anglican communion, but in common usage the term refers to the Roman Catholic Church.
Many of those, who apply the term "catholic church" to all Christians indiscriminately, object to this use of the term to designate what they view as only one denomination within what they see as the "whole" catholic Church. However, the Roman Catholic Church, both in its Western form and in that of the Eastern Catholic Churches, always considered itself to be the Catholic Church, with all others as "non-Catholics", and regularly refers to itself as "the Catholic Church". This practice is in application of the belief that not all who claim to be Christians are part of the Catholic Church, as Ignatius of Antioch, the earliest known writer to use the term "Catholic Church", considered that certain heretics who called themselves Christians only seemed to be such. Though normally distinguishing itself from other churches by calling itself the "Catholic Church", it accepts the description "Roman Catholic Church". Even apart from documents drawn up jointly with other churches, it has sometimes, in view of the central position it attributes to the See of Rome, adopted the adjective "Roman" for the whole Church, Eastern as well as Western, as in the papal encyclicals Divini illius Magistri and Humani generis. Another example is its self-description as the "Holy, Catholic, Apostolic and Roman Church" in the 24 April 1870 Dogmatic Constitution on the Catholic Faith of the First Vatican Council. In all of these documents it also refers to itself simply as the Catholic Church and by other names. The Eastern Catholic Churches, while united with Rome in the faith, have their own traditions and laws, differing from those of the Latin Rite and those of other Eastern Catholic Churches.
The Eastern Orthodox Church also identifies itself as Catholic , as in the title of The Longer Catechism of the Orthodox, Catholic, Eastern Church. This Church and also Oriental Orthodoxy and the Assyrian Church of the East all see themselves as the "one holy catholic and apostolic Church" of the Nicene Creed.
Anglicans and Old Catholics see themselves as a communion within that one church, and Lutherans see themselves as "a reform movement within the greater Church catholic".
Roman Catholics view the Bishop of Rome as the "Successor of Peter" to serve as universal pastor to the entire Church. Eastern Orthodox Christians do recognize the primacy of the Bishop of Rome (i.e., the Pope) but only in the sense of a primacy of honour, not one of jurisdiction, among the Patriarchates of Constantintinople, Alexandria, Antioch and Jerusalem. Anglicans and Old Catholics accept that the Bishop of Rome is primus inter pares among all primates, but they embrace Conciliarism as a necessary check on what they consider to be the "excesses" of Ultramontanism.
Roman Catholics, Orthodox Christians (in general) and the Assyrian Church of the East each recognize the "validity" of each other's Eucharist (Mass or Divine Liturgy), and of the holy orders of their respective priesthoods and episcopate. The Roman Catholic Church, on the other hand, considers Anglican holy orders to be "null and void", as declared by Pope Leo XIII in the papal bull Apostolicae curae. Beginning with the encyclical letter Saepius officio of the Archbishops of Canterbury and York in response to Apostolicae curae, Anglicans have steadfastly rejected this claim. At present Old Catholics are in full communion with the worldwide Anglican Communion, including full exchange of clergy and participation in each other's ordinations (including episcopal consecrations). Some Lutheran churches are also in communion with some Anglican provinces. Although there were some statements made by Orthodox leaders in the early 20th century giving hope to Anglican clergy that their priestly orders would eventually be recognized as valid by the Orthodox, today there is little variance among Orthodox patriarchs and metropolitans on the validity of Anglican orders. As with the Roman Catholic Church, today the Orthodox churches universally require ordination to the priesthood for Anglican clergy who convert to Orthodoxy.
Thus, for example, in an emergency, when no Roman Catholic priest is available, a Roman Catholic may, under canon law, receive the Holy Eucharist and receive absolution from an Orthodox priest, but not from an Anglican priest. This also means that if an Anglican male priest becomes a Roman Catholic, the Roman Catholic Church may confer ordination on him (in its view, for the first time). While the Roman Catholic belief that holy orders cannot be conferred on women holds even in the case of ordinations in churches, such as the Old Catholic Church, the validity of whose orders in male clergymen is not denied, some Anglican provinces have adopted ordination of women. These practices constitute a considerable block to greater unity, in spite of substantial progress in ecumenical dialogues between Anglicans and Roman Catholics since the Second Vatican Council.
Recent historic ecumenical efforts on the part of Roman Catholic Church have focused on healing the rupture between the Western ("Catholic") and the Eastern ("Orthodox") churches. Pope John Paul II often spoke of his great desire that the Catholic Church "once again breathe with both lungs",  thus emphasizing that the Roman Catholic Church seeks to restore full communion with the separated Eastern churches.
After the East-West Schism, conventionally dated to 1054, a brief reunification took place in the mid-15th century at the Council of Florence. The present pope, Benedict XVI, has stated his wish to restore full unity with the Orthodox. The Roman Catholic Church considers that almost all of the ancient theological differences have been satisfactorily addressed (the Filioque clause, the nature of purgatory, etc.), and that recent practice with regard to the Eastern Catholic churches in communion with Rome, especially since the Second Vatican Council, has shown that a reunion will not mean "Latinization" of the Eastern churches.
Methodists and Presbyterians believe their denominations owe their origins to the Apostles and the early church, but do not claim descent from ancient church structures such as the episcopate. However, both of these churches hold that they are a part of the catholic (universal) church.
Some Protestant churches avoid using the term completely, to the extent among many Lutherans of reciting the Creed with the word Christian in place of catholic.    The Orthodox churches share some of the concerns about Roman Catholic papal claims, but disagree with some Protestants about the nature of the church as one body. For some, to use the word "catholic" at all is to appear to give credence to papal claims.