It was in 1937 that Fr Congar's first book was published: Disunited Christians: Principles for a Catholic Ecumenism. This book called for dialogue among Christians with a view to a renewal of the church. Fifty years later, and twenty-five years after the Second Vatican Council, the church is very different. It has a new awareness of itself and its different charisms and ministries. There are those who have spoken of the changes that have taken place as a break with the earlier period marked by the Council of Trent; others stress that they are innovations within a degree of continuity. Fr Congar, who was a peritus at Vatican II and has much theological study and writing behind him, can bring both historical knowledge and a deep spiritual understanding to the developments which have taken place in his lifetime. In these conversations he comments on a wide range of theological issues, including authority in the church, the role of the Pope, liberation theology, Christianity and other religions, the numerical decline of the priesthood, the role of the laity, and the right to differ within the church.