It has become almost a cliche to use the term ""most important"" when referring to Father Congar's numerous works on a variety of subjects. Yet, once again, one is forced to say that Dialogue Between Christians is the most important work yet to appear, or likely to appear in the foreseeable future, on the movement toward union between the Christian Churches. Congar's authority as the most distinguished theologian of Catholicism is reinforced, in this work, by the 30-odd years spent in pioneering the ecumenical movement, at a time when it was not considered respectable, or even quite ""safe."" The book traces the history of ecumenism throughout the world, and then concentrates on a detailed, realistic and objective discussion of the obstacles and incentives to union between the Protestant Churches and the Church of Rome. This is an indispensable addition to every library with even a small religious section. It will undoubtedly become one of the classics of modern religious literature.