The four great conciliar constitutions, On the Sacred Liturgy, On Divine Revelation, On the Church, and On the Church in the Modern World, have set down principles which will shape the life of the Church for decades, if not centuries. Not only did the Council ratify and approve what the leading catechists had been saying about the need to harmonize teaching and life, but it went far beyond their visions and opened up new horizons and perspectives. Because of this it was necessary to rethink, reorganize, and considerably expand Part Two of previous editions. . . Besides the major conciliar constitutions, the decrees On the Bishops’ Pastoral Office, On the Apostolate of the Laity, On the Church’s Missionary Activity, and to some extent the Declaration on Christian Education, were discussed and applied to catechetics by the International Study Weeks of Bangkok, Katigondo, and Manila in 1962, 1964, and 1967. Much of the thinking of these groups is reflected in a new chapter which has been added to Part One, “The Impact of the Missions on Catechetics,” as well as in some selections from their conclusions, which have been added to the appendix. The Decree on Priestly Formation made it possible for us to omit a chapter on the role of kerygmatic theology in priestly formation, which had appeared in previous editions. . .