A person is brought into full communion with the Catholic Church through reception of the three sacraments of Christian initiation—baptism, confirmation, and the holy Eucharist—but the process by which one becomes a Catholic can take different forms.

A person who is baptized in the Catholic Church becomes a Catholic at that moment. One's initiation is deepened by confirmation and the Eucharist, but one becomes a Catholic at baptism. This true both for children who are baptized Catholic (and receive the other two sacraments later) and for adults who are baptized, confirmed, and receive the Eucharist at the same time.

Those who have been validly baptized outside the Catholic Church become Catholics by making a profession of the Catholic faith and being formally received into the Church. This is normally followed immediately by confirmation and the Eucharist.

Before a person is ready to be received into the Catholic Church, whether by baptism or by profession of faith, preparation is necessary. The amount and the form of this preparation depends on the individual's circumstance. The most basic division in the kind of preparation needed is between those who are unbaptized and those who have already become Christian through baptism in different denominations.

For adults and children who have reached the age of reason (age seven), entrance into the Church is governed by the Rite of Christian Initiation for Adults (RCIA).

Preparation for reception into the Church begins with the inquiry stage, in which the unbaptized person begins to learn about the Catholic faith and begins to decide whether to embrace it.

The first formal step on the road to becoming a Catholic takes place with the rite of reception into the order of catechumens, in which the unbaptized express their desire and intention to become Christians. "Catechumen" is a term the early Christians used to those preparing to be baptized and become Christians.

The period of catechumenate lasts for a variable period of time—sometimes even years, though that is very unusual—depending on how much the catechumen has learned and how ready the catechumen feels to take the step of becoming a Christian. However, the catechumenate often lasts for something much less than a year.

The purpose of the catechumenate is to provide the candidates with a thorough background in Christian teaching. A thoroughly comprehensive catechesis on the truths of Catholic doctrine and moral life, aided by approved catechetical texts, is to be provided during the period of the catechumenate. The catechumenate is also intended to give the candidates the opportunity to reflect upon and firm up their desire to become Catholics, and to give them the chance to show that they are ready to take this serious step (cf. Luke 14:27-33; 2 Pet. 2:20-22).

The second formal step is taken with the rite of election, in which the catechumens' names are written in a book of those who will receive the sacraments of initiation. At the rite of election, the catechumen again expresses the desire and intention to become a Christian, and the Church judges that the catechumen is ready to take this step. Normally, the rite of election occurs on the first Sunday of Lent, the forty day period of preparation for Easter.

After the rite of election, the candidates undergo a period of more intense reflection, purification, and enlightenment, in which they deepen their commitment to repentance and conversion to the Christian faith. During this period the candidates, now known as the elect, participate in several further rituals.

The three chief rituals, known as "scrutinies," are normally celebrated at Mass on the third, fourth, and fifth Sundays of Lent. The scrutinies are rites for self-searching and repentance. They are meant to bring out the qualities of the candidate's soul, to heal those qualities which are weak or sinful, and to strengthen those which are positive and good.

Normally during this period, the candidates are also formally presented with the Apostles' Creed and the Lord's Prayer, both of which they will recite on the night they are initiated.

The initiation itself usually occurs on Easter Vigil, the evening before Easter Day. That evening a special Mass is celebrated at which the candidates are baptized, then given confirmation, and finally receive the holy Eucharist. At this point the candidates become Catholics and are received into full communion with the Church.

Ordinarily the bishop oversees the Easter Vigil service and confers confirmation upon the candidates, but often—due to large distances or numbers of candidates—a local parish priest may be granted permission from the bishop to perform these rites.

The final state of Christian initiation is known as mystagogy, in which the new Christians are strengthened in the faith by further instruction and become more deeply rooted in the local Catholic community. The period of mystagogy normally lasts throughout the Easter season (the fifty days between Easter and Pentecost Sunday).

For the first year of their life as Christians, those who have been received are known as "neophytes" or "new Christians."

The means by which those who have already been validly baptized become part of the Church differs considerably from that of the unbaptized.

Because they have already been baptized, they are already Christians and are not catechumens. Because they have already become Christians, the Church is very concerned that they not be confused with those who are still in the process of becoming Christians.  "The term 'catechumen' should be strictly reserved for the unbaptized who have been admitted to the order of catechumens . . . and never used of those baptized Christians who are received into the full communion of the Catholic Church."

"Those who have already been baptized in another Church or ecclesial community should not be treated as catechumens or so designated. Their doctrinal and spiritual preparation for reception into full Catholic communion should be determined according to the individual case, that is, it should depend on the extent to which the baptized person has led a Christian life within a community of faith and been appropriately catechized to deepen his or her inner adherence to the Church."

For those who were baptized but who have never been instructed in the Christian faith or lived as Christians, it is appropriate for them to receive much of the same instruction in the faith as catechumens, but they are still not catechumens and are not to be referred to as such. As a result, they are not to participate in the rites intended for catechumens, such as the scrutinies. Even "the rites of presentation of the creed, the Lord's Prayer, and the book of the Gospels are not proper except for those who have received no Christian instruction and formation."

For those who have been instructed in the Christian faith and have lived as Christians the situation is different. The U.S. Conference of Bishops states: "Those baptized persons who have lived as Christians and need only instruction in the Catholic tradition and a degree of probation within the Catholic community should not be asked to undergo a full program parallel to the catechumenate."  For this reason they should not share in the same, full RCIA programs that catechumens do.

The timing of their reception into the Church is also different. The U.S. Conference of Bishops states: "It is preferable that reception into full communion not take place at the Easter Vigil lest there be any confusion of such baptized Christians with the candidates for baptism, possible misunderstanding of or even reflection upon the sacrament of baptism celebrated in another Church or ecclesial community . . . "

Rather than being received on Easter Vigil, "the reception of candidates into the communion of the Catholic Church should ordinarily take place at the Sunday Eucharist of the parish community, in such a way that it is understood that they are indeed Christian believers who have already shared in the sacramental life of the Church and are now welcomed into the Catholic Eucharistic community . . . "

It is therefore important for Christians coming into the Catholic Church to coordinate carefully with their local pastor and/or bishop concerning the amount of Catholic instruction they need and the exact timing of their reception into the Church.

The sacrament of baptism removes all sins committed prior to it, but since Christians have already received this sacrament, it is necessary for them to confess mortal sins they have committed since baptism before receiving confirmation and the Eucharist. In some cases, this can be difficult due to a large number of years between the Christian's baptism and reception into the Catholic Church. In such cases, the candidate should confess the mortal sins he can remember by kind and, to the extent possible, indicate how often such sins were committed (as always with the sacrament of reconciliation, the absolution covers any mortal sins that could not be remembered, so long as the recipient intended to repent of all mortal sins).

Christians coming into the Church should be encouraged to receive reconciliation frequently while waiting to be received: "The celebration of the sacrament of reconciliation with candidates for reception into full communion is to be carried out at a time prior to and distinct from the celebration of the rite of reception. As part of the formation of such candidates, they should be encouraged in the frequent celebration of this sacrament."

The Christian fully enters the Church by profession of faith and formal reception. For the profession of faith, the candidate says: "I believe and profess all that the holy Catholic Church believes, teaches, and proclaims to be revealed by God." The bishop or priest then formally receives the Christian into the Church by saying, "[Name], the Lord receives you into the Catholic Church. His loving kindness has led you here, so that in the unity of the Holy Spirit you may have full communion with us in the faith that you have professed in the presence of this his family."

The bishop then normally administers the sacraments of confirmation and celebrates the holy Eucharist, giving the new Catholic the Eucharist for the first as a Catholic time.

In some situations, there may be a doubt concerning whether a person's baptism was valid. All baptisms are assumed valid, regardless of denomination, unless after serious investigation there is reason to doubt that the candidate was baptized with water and the Trinitarian formula (". . . in the name of the Father and of the Son and of the Holy Spirit") or that the minister or recipient of baptism did not intend it to be an actual baptism.

If there is reason to doubt whether a person's baptism was valid (or whether the person was baptized at all), then the candidate will be given a conditional baptism (one with the form, ". . . if you are not already baptized, I baptize you in the name of the Father and of the Son and of the Holy Spirit").

"If conditional baptism . . . seems necessary, this must be celebrated privately rather than at a public liturgical assembly of the community and with only those limited rites which the diocesan bishop determines. The reception into full communion should take place later at the Sunday Eucharist of the community."

Another special case is that of those who have been baptized as Catholics but who not been brought up in the faith or not received the sacraments of confirmation and the Eucharist. "Although baptized adult Catholics who have never received catechetical instruction or been admitted to the sacraments of confirmation and Eucharist are not catechumens, some elements of the usual catechumenal formation are appropriate to their preparation for the sacraments, in accord with the norms of the ritual, 'Preparation of Uncatechized Adults for Confirmation and Eucharist.'"

A final case is that of Catholics who received confirmation and the Eucharist but who left the Church by a formal act, such as joining another church or denomination. Normally individuals in this situation can come back to the Church and become Catholics again by going to confession and being reconciled. Unless there are complicating circumstances, most priests have the faculty to receive people back into the Church in this manner.

It can be a time of anxious longing while one waits to feel the warm embrace of the Church and to be immersed into Catholic society. This time of waiting and reflection is necessary, since becoming a Catholic is a momentous event of great importance, but waiting can be quite painful as one looks forward with anticipation to the sacraments, especially the Eucharist, and to the joys of Catholic life—the strength and security that being a faithful Catholic bestows on one's life. Yet even before being received, those waiting to be incorporated already have a very real and very special relationship with the Church.

In the case of those who are already Christians, their baptism itself forms a certain sacramental relationship with the Church. They are also joined to the Church by their very intention to enter it, as are the unbaptized who intend to do so: "Catechumens who, moved by the Holy Spirit, desire with an explicit intention to be incorporated into the Church are by that very intention joined to her. With love and solicitude mother Church already embraces them as her own."

Thus even before one is fully incorporated into the Church, one can already enjoy the status of being recognized by the Church as one of her own, precious children.