CATECHISM. A popular manual of instruction in Christian doctrine. In the early Church, catechetical instruction was standardized in preparation for baptism as in the writings of St. Augustine (354-430) and St. Gregory of Nyssa (330-95). After the invention of printing, books of catechetical instruction multiplied. The best known catechisms in the Catholic Church are St. Peter Canisius' Summa of Christian Doctrine (1555) and the Catechism of the Council of Trent, or Roman Catechism (1566). Numerous catechisms were published in various countries authorized by their respective hierarchies, e.g., the so-called Penny Catechism in Great Britain and the series of Baltimore Catechisms in the United States. Since the Second Vatican Council, all catechisms published by ecclesiastical authority must also be "submitted to the Apostolic See for review and approval" (General Catechetical Directory, 119).