Catechism of the Catholic Church §1247 — excerpt
Since the beginning of the Church, adult Baptism is the common practice where the proclamation of the Gospel is still new. the catechumenate (preparation for Baptism) therefore occupies an important place.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.