During the Catholic Counter-Reformation, the Council of Trent commissioned the Roman Catechism (or Catechism of the Council of Trent, published 1566) to expound doctrine and to improve the theological understanding of the clergy. It differs from other summaries of Christian doctrine for the instruction of the people in two points: it is primarily intended for priests having care of souls (ad parochos), and it enjoyed an authority within the Catholic Church equalled by no other catechism until the Catechism of the Catholic Church (1992). The need of a popular authoritative manual arose from a lack of systematic knowledge among pre-Reformation clergy and the concomitant neglect of religious instruction among the faithful.

The Council intended the projected Catechism to be the Church's official manual of popular instruction. The seventh canon, "De Reformatione", of Sess. XXIV, runs: "That the faithful may approach the Sacraments with greater reverence and devotion, the Holy Synod charges all the bishops about to administer them to explain their operation and use in a way adapted to the understanding of the people; to see, moreover, that their parish priests observe the same rule piously and prudently, making use for their explanations, where necessary and convenient, of the vernacular tongue; and conforming to the form to be prescribed by the Holy Synod in its instructions (catechesis) for the several Sacraments: the bishops shall have these instructions carefully translated into the vulgar tongue and explained by all parish priests to their flocks . . .". In the mind of the Church the Catechism, though primarily written for the parish priests, was also intended to give a fixed and stable scheme of instruction to the faithful, especially with regard to the means of grace, so much neglected at the time. To attain this object the work closely follows the dogmatic definitions of the council. It is divided in four parts:

I. The Apostles' Creed;
II. The Sacraments;
III. The Decalogue;
IV. Prayer, especially The Lord's Prayer.

It deals with the papal primacy and with Limbo, points which were not discussed or defined at Trent; on the other hand, it is silent on the doctrine of Indulgences, which is set forth in the "Decretum de indulgentiis", Sess. XXV. The bishops urged in every way the use of the new Catechism; they enjoined its frequent reading, so that all its contents would be committed to memory; they exhorted the priests to discuss parts of it at their meetings, and insisted upon its being used for instructing the people.

To some editions of the Roman Catechism is prefixed a "Praxis Catechismi", i.e. a division of its contents into sermons for every Sunday of the year adapted to the Gospel of the day. There is no better sermonary. The people like to hear the voice of the Church speaking with no uncertain sound; the many Biblical texts and illustrations go straight to their hearts, and, best of all, they remember these simple sermons better than they do the oratory of famous pulpit orators. The Catechism has not of course the authority of conciliary definitions or other primary symbols of faith; for, although decreed by the Council, it was only published a year after the Fathers had dispersed, and it consequently lacks a formal conciliary approbation. During the heated controversies de auxiliis gratiae between the Thomists and Molinists, the Jesuits refused to accept the authority of the Catechism as decisive. Yet it possesses high authority as an exposition of Catholic doctrine. It was composed by order of a council, issued and approved by the pope; its use has been prescribed by numerous synods throughout the whole Church; Leo XIII, in a letter to the French bishops (8 Sept., 1899), recommended the study of the Roman Catechism to all seminarians.