It is surely no accident that the two most important books to be discussed here are products of the ecumenical debate; they are important, that is, not merely for professional ‘ecumenicists’ but for theologians generally. The point made by Père Congar many years ago, that Catholic theologians have something to learn from non-Catholic theology, is being verified in particular examples of constructive theological work, in a response to the insights of faithful dissident Christians which takes those insights seriously and positively and seeks critically to assimilate them into a fuller Catholic theology rather than to controvert them merely from what can now be recognized as often too narrow a basis. How intimate the debate has become abroad may be seen from the remarkable collection of studies offered to Otto Karrer on his seventieth birthday, edited by Maximilian Roesle, O.S.B., and Oscar Cullmann. In this large volume of nearly seven hundred pages, Catholic and Protestant writers pair off with each other to study in turn topics which have for centuries been regarded as purely controversial; Catholic writers include Vögtle, Schlier, Geiselmann, Küng, Jedin, Mörsdorf, Fries, Alois Müller, Sartory, and among the Protestants are Asmussen, Stauffer, von Allmen, Stählin, to mention only names known to me. The long study of Peter and the ‘rock’ text by the Protestant Johannes Ringger is particularly striking; it is an extraordinary fact that Catholic theologians, even since the appearance of Cullmann’s Peter (recently published in a revised German edition), have been much more interested in the apologetic case for Peter than in his theological significance, which is not, after all, exhausted in the Vatican decrees which define it.