The ground-breaking treatment of the doctrine of the Trinity by one of the most important theologians of the century is here reprinted on the 30th anniversary of its orginal publication. In this treatise, Karl Rahner analyzes the place of the doctrine of the Trinity within Catholic theology and develops his own highly original and innovative reading of the doctrine, including his now-famous dictum. Karl Rahner (1904-1984) was on of the most important and influential Roman Catholic thinkers of the twentieth century. A major influence and the Second Vatican Council his extensive writings have inspired generations of modern students.