There is a large and growing number of people, both Catholic and Protestant, who are coming to recognize Karl Rahner, S.J., as the most important Roman Catholic theologian of the present period. While a number of books and articles on Rahner are beginning to appear, most of them are limited simply to expositing his position. What has yet to be done in a satisfactory way is to think through critically his relationship to and significance for the wider theological enterprise, that is, in terms of the interconfessional discussion (as well as in terms of current secular reflection upon general human experience). Rahner's work deserves such consideration, although, because of the fact that since the Reformation and Vatican I Protestant and Catholic thought have tended to develop independently of each other, it is difficult for one schooled sufficiently in Rahner's tradition to understand his work to understand Protestant thought sufficiently well to make a discussion meaningful, and the opposite situation is also the case. Without claiming exemption from this handicap, I should like to make a beginning at the sort of clarification and critical analysis that seems to me to be needed.