Canonization is the act by which a particular Christian church declares a deceased person to be a saint and is included in the canon, or list, of recognized saints. Originally, individuals were recognised as saints without any formal process.
In the Roman Catholic Church and the Eastern Catholic Churches in communion with Rome, the act of canonization is reserved to the Holy See and occurs at the conclusion of a long process requiring extensive proof that the person proposed for canonization lived and died in such an exemplary and holy way that he or she is worthy to be recognized as a saint. The church's official recognition of sanctity implies that the persons are now in heavenly glory, that they may be publicly invoked and mentioned officially in the liturgy of the church, most especially in the Litany of the Saints in the Canon of the Mass. Other Christian churches still follow the older practice (see, for instance, below on Eastern Orthodox practice).
Canonization, whether formal or informal, does not make someone a saint: it is only a declaration that the person is a saint and was a saint even before canonization. It is generally believed that there are many more saints in heaven than have been canonized on earth.
By the fourth century, however, "confessors", people who had confessed their faith not by dying but by word and life, began to be venerated publicly. Examples of such people are Saint Hilarion and Saint Ephrem the Syrian in the East, and Saint Martin of Tours and Saint Hilary of Poitiers in the West. Their names were inserted in the diptychs, the lists of saints explicitly venerated in the liturgy, and their tombs were honoured like those of the martyrs. Since the witness of their lives was not as unequivocal as that of the martyrs, they were venerated publicly only with the approval by the local bishop.
This approval was required even for veneration of a reputed martyr. In his history of the Donatist heresy, Saint Optatus recounts that at Carthage a Christian matron, named Lucilla, incurred the censures of the Church for having kissed the relics of a reputed martyr whose claims to martyrdom had not been juridically proved. And Saint Cyprian (died 258) recommended that the utmost diligence be observed in investigating the claims of those who were said to have died for the faith. All the circumstances accompanying the martyrdom were to be inquired into; the faith of those who suffered, and the motives that animated them were to be rigorously examined, in order to prevent the recognition of undeserving persons. Evidence was sought from the court records of the trials or from people who had been present at the trials.
Saint Augustine of Hippo (died 430) tells of the procedure which obtained in his day for the recognition of a martyr. The bishop of the diocese in which the martyrdom took place set up a canonical process for conducting the inquiry with the utmost severity. The acts of the process were sent either to the Metropolitan or Primate, who carefully examined the cause, and, after consultation with the suffragan bishops, declared whether the defunct was worthy of the name of 'martyr' and public veneration. Acts of formal recognition, such as the erection of an altar over the saint's tomb or transferring the saint's relics to a church, were preceded by formal inquiries into the sanctity of the person's life and the miracles attributed to that person's intercession. Such acts of recognition of a saint were authoritative, in the strict sense, only for the diocese or ecclesiastical province for which they were issued, but with the spread of the fame of a saint, were often accepted elsewhere also.
The Holy See began to be asked to intervene, so as to ensure a more authoritative decision. The canonization of Saint Udalric, Bishop of Augsburg, by Pope John XV in 993 is the first undoubted example of a papal canonization of a saint from outside Rome. (Some historians maintain that the first such canonization was that of Saint Swibert by Pope Leo III in 804.) Thereafter recourse was had with greater frequency to the judgment of the Popes. Walter of Pontoise was canonized by Hugh de Boves, the Archbishop of Rouen in 1153; Walter was the last saint in Western Europe to have been canonized by an authority other than the Pope. “The last case of canonization by a metropolitan is said to have been that of St. Gaultier, or Gaucher, abbat of Pontoise, by the Archbishop of Rouen, A.D. 1153. A decree of Pope Alexander III, A.D. 1170, gave the prerogative to the pope thenceforth, so far as the Western Church was concerned.”
In 1173 Pope Alexander III, after reprimanding certain bishops for having permitted veneration of a man who was far from being a saint, decreed: "You shall not therefore presume to honour him in the future; for, even if miracles were worked through him, it is not lawful for you to venerate him as a saint without the authority of the Catholic Church.
The procedure initiated by the text of Alexander III, confirmed by a bull of Pope Innocent III in the year 1200, issued on the occasion of the canonization of Saint Cunegunde, led to increasingly elaborate inquiries.
"Servant of God" The process leading towards canonization begins at the diocesan level. A bishop with jurisdiction - usually the bishop of the place where the candidate died and/or is buried, although another ordinary can be given this authority - gives permission to open an investigation into the virtues of the individual, responding to a petition by members of the faithful, either actually or pro forma. This investigation may open no sooner than five years after the death of the person being investigated. However, the pope has the authority to waive this five year waiting period, as was done for Mother Teresa by Pope John Paul II and for John Paul II himself by his immediate successor, Benedict XVI. Normally, a guild or organization to promote the cause of the candidate's sainthood is created, an exhaustive search of the candidate's writings, speeches and sermons is undertaken, a detailed biography is written and eyewitness accounts are gathered. When sufficient information has been gathered, the investigation of the candidate, who is called "Servant of God", is presented by the local bishop to the Roman Curia—the Congregation for the Causes of the Saints—where it is assigned a postulator, whose task is to gather further information about the life of the Servant of God. Religious orders who regularly deal with the congregation often have their own designated postulator generals.
"Declaration 'Non Cultus'" At some point, permission is then granted for the body of the Servant of God to be exhumed and examined, a certification ("non cultus") that no superstitious or heretical worship or improper cult has grown up around the servant or his or her tomb is made, and relics are taken.
"Venerable/Heroic in Virtue" When enough information has been gathered, the congregation will recommend to the pope that he make a proclamation of the Servant of God's heroic virtue (that is, that the servant exhibited the theological virtues of faith, hope and charity, and the cardinal virtues of prudence, justice, fortitude and temperance, to an heroic degree). From this point the one said to be "heroic in virtue" is referred to by the title "Venerable". A Venerable has as of yet no feast day, no churches may be built in his or her honor, and the church has made no statement on the person's probable or certain presence in heaven, but prayer cards and other materials may be printed to encourage the faithful to pray for a miracle wrought by his or her intercession as a sign of God's will that the person be canonized.
"Blessed" Beatification is a statement by the church that it is "worthy of belief" that the person is in heaven, having come to salvation. This step depends on whether the Venerable is a martyr or a "confessor".
For a martyr, the pope has only to make a declaration of martyrdom, a certification that the venerable gave his or her life voluntarily as a witness for the faith and/or in an act of heroic charity for others. This allows beatification, giving the venerable the new title "Blessed" (abbreviated "Bl.") or, in Latin, Beatus or Beata. A feast day will be designated, but its observance is normally restricted to the Blessed's home diocese, to certain locations associated with him or her, and/or to the churches or houses of the blessed's religious order, if they belonged to one. Parishes may not normally be named in honor of a Blessed.
If the Venerable was not a martyr - all non-martyrs are "confessors" as they "confessed" or bore witness to their faith by how they lived their lives - it must be proven that a miracle has taken place by his or her intercession - that is, that God has shown a sign that the person is enjoying the Beatific Vision by God performing a miracle in response to the Blessed's prayers. Today, these miracles are almost always miraculous cures, as these are the easiest to establish based on the Catholic Church's requirements for a "miracle." (The patient was sick, there was no known cure for the ailment, prayers were directed to the Venerable, the patient was cured, the cure was spontaneous, instantaneous, complete and lasting, and doctors cannot find any natural explanation.)
"Saint" (abbreviated "St." and "St") To be canonized a saint, one (more) miracle is necessary. Canonization is a statement by the church that the person certainly enjoys the Beatific Vision. The saint is assigned a feast day which may be celebrated anywhere within the Catholic Church, although it may or may not appear on the general calendar or local calendars as an obligatory feast, parish churches may be built in his or her honor, and the faithful may freely and without restriction celebrate and honor the saint.
In the case of persons that common usage has called saints from "time immemorial" (in practice, since before 1500 or so), the Church may carry out a "confirmation of cultus", which is much simpler. For example, Saint Hermann Joseph had his veneration confirmed by Pope John Paul II.
In the case of the Eastern Catholic Churches, individual churches sui juris retain, in theory, the right to glorify (see next section on Eastern Orthodox practice) saints for their own jurisdictions, though this has rarely happened in practice.
Although a recognition of sainthood by the pope does not directly concern a fact of divine revelation, it must still be "definitively held" by the faithful as infallible under (at the very least) the Universal Magisterium of the Church since it is a truth connected to revelation by historical necessity.
Glorification of saints in the Eastern Orthodox Church differs from Roman Catholic tradition in both theology and practice. The Glorification of saints is considered to be an act of God, not a declaration of the hierarchy. The official recognition of saints grows from the consensus of the church.
When an individual who has been sanctified by the grace of the Holy Spirit falls asleep in the Lord, God may or may not choose to glorify the individual through the manifestation of miracles. If so, the devotion to the saint will normally grow from the "grass roots" level. Eventually, miracles will have grown to such a degree that a formal Service of Glorification will be scheduled. A Glorification may be performed by any Bishop within his Diocese. Often there will be a formal investigation to be sure that the individual is Orthodox in their faith, has led a life worthy of emulation, and that the reports of miracles attributed to their intercessions are verifiable. The Glorification service does not "make" the individual a saint; rather, the Church is simply making a formal acknowledgement of what God has already manifested.
Martyrs need no formal Glorification; the witness of their self-sacrifice is sufficient.