The Rite of Christian Initiation of Adults (RCIA) is a process of formation and celebration through which adults (and children who have reached the age of reason) are fully initiated into the Catholic faith community. It involves four periods of formation.

1. Period of Inquiry. This is a somewhat informal period where the person begins to develop an interest in the Catholic faith and to inquire about the faith. Such a person may have Catholic friends to whom they dialogue with, or they may have begun reading about the faith and wish to learn more. The next step is to enter the more formal and structured RCIA program offered by the parish.
This period ends with a celebration at a Sunday called the Rite of Acceptance for the unbaptized combined with the Rite of Welcoming for the already baptized.

The Rite of Acceptance, combined with the Rite of Welcoming, is a ritual in which those who are ready are accepted as catechumens or candidates in the Catholic Church. It is a formal declaration proclaiming their intent to be received into the Catholic Church. The catechumens and candidates are signed with a cross on their foreheads, ears, eyes, lips, shoulders, and hands as a sign of their readiness to bear witness to Christ with their whole lives.

2. Period of the Catechumenate. This period involves formal instructions about the Catholic faith. Topics covered include: Divine Revelation, Sacred Tradition, Sacred Scripture, the Magisterium, Who  Jesus Christ Is;  the Paschal Mystery, Church History, Justification and Grace,  the Mystery of the Church, Mary and the Saints, Purgatory, Heaven, and Hell, the Sacraments, Christian Morality, and more. 

The period ends with the Rite of Election (catechumens).  The Rite of Election takes place either on the 1st Sunday of Lent of the 2nd Sunday of Lent. 

3. Period of Purification and Enlightenment. The third period is called the Period of Purification and Enlightenment. Some catechesis will continue in the period, but the main focus in on preparation to receive the Sacraments of initiation (Baptism, Confirmation, and Eucharist) at the Easter Vigil.

4. Period of Postbaptismal Catechesis. The fourth period is called Period of Postbaptismal Catechesis or Mystagogy. It is a time for deepening the Christian experience, for gaining spiritual fruit, and for entering more closely into the life and unity of the community of the faithful. This period continues for several weeks after the Easter Vigil.