Yves Congar, OP, who died in 1995, was a French Dominican widely recognized as one of the most important Roman Catholic theologians of the twentieth century and a major influence upon the theology of the documents of Vatican II. Congar drew from biblical, patristic, and medieval sources to revitalize the discipline of contemporary theology. He was an early advocate of ecumenism and also contributed to shaping the theological agenda of the twentieth-century liturgical movement. He was named a cardinal in 1994 by Pope John Paul II. Liturgical Press has also recently published At the Heart of Christian Worship: Liturgical Essays of Yves Congar and Congar's classic work True and False Reform in the Church. Paul Philibert, OP, has taught pastoral theology in the United States and abroad. He is a Dominican friar of the Southern Province. His translation of a collection of Congar's essays on the liturgy has been published by Liturgical Press under the title At the Heart of Christian Worship. His book The Priesthood of the Faithful: Key to a Living Church (Liturgical Press, 2005) reflects the ecclesiology of Yves Congar and his vision of the apostolic life of the faithful.