Catechism (Gr.Catechism 040066 instruction), in a general and modern sense, an elementary text book of any science or art. More commonly, however, it means a text book for the instruction of the catechumens and children of a parish or congregation in the doctrines of the church, or the moral precepts of Christianity. The original form of this instruction was oral, by question and answer. The practice was to gather those who needed instruction into some suitable place, and there persons qualified either held disputations or delivered dogmatic lectures, and then questioned the hearers upon what had been said. It is probable that the early catechists followed no set forms, but endeavored, by catechising their hearers, to awaken a train of thought, and then followed it whithersoever it might lead. But when the doctrinal theology of the church became more strictly defined, catechetical instruction became more dogmatic. These compends have of course varied with the variations of theological opinion in different ages and communions.

A formula of doctrine, the Catechismus Romanus, was drawn up by order of the council of Trent, and published at Rome in 1566, under the sanction of Pope Pius V., and was subsequently approved by special bulls and adopted by vote of provincial synods in various Catholic countries. It was ordered that it should be faithfully translated into the vernacular languages, and expounded to the people by all pastors. But it was designed as a directory for the use of the clergy rather than as a system of popular instruction. It was not originally in the form of question and answer, though some later editions are in that shape. In common use in various parts of the Catholic world were the catechisms drawn up by Canisius (1554 and 1566), by Bellarmin (1603), and by Bossuet (1687). A catechism designated as Schema de Parvo, essentially that of Bellarmin, was decreed by the oecumenical council at Rome in 1870, its object being to provide a common catechism for the whole church. Strictly speaking, the Greek church has no authorized catechism; but that of Mogilas, metropolitan of Kiev (1642), was in 1672 recognized as a standard by a synod at Jerusalem. The principal Protestant catechisms are those of Luther (1529) and Calvin (1536); the Heidelberg catechism (1562), on the basis of which the Zurich catechism was drawn up (1639) for the Reformed church of Germany; that of the Socinians, published at Rakow (1574 and 1008); that of the English church, the work probably of Cranmer (1549), with the exception of that part which relates to the sacraments, which was added by Bishop Overall in the first year of James I., after the conference of Hampton court; and that of the Westminster assembly, longer and shorter (1043), which serves as a basis for the Calvinistic and Presbyterian churches both of Great Britain and the United States. There are many mediaeval writings and documents bearing the name of catechisms, which if collected together would form a work similar to the collections already made of old liturgies and hymns.

The private or individual catechisms of German theologians are numerous, and many of them voluminous, thus departing from the primitive idea of the Christian catechism as an instrument for popular and elemental instruction.