When the Swedish theologian George Hammar in his study of Reinhold Niebuhr tried to formulate concisely the standpoint of this religious thinker, he did so in the very words he used in the title ‘Christian Realism’.1 He thus employed a term which is used elsewhere to characterise Niebuhr's theological thinking and which is a favourite with Niebuhr himself. This term, of course, is used so often in current theological discussions and with so many different associations, as to have become rather ambiguous and vague. The use of it here does not aspire to anything more than to indicate roughly the theology which tries to show its disagreement with ethical idealism in ‘Christian practice’ and with idealistic religious philosophy in ‘Christian theory’;. Both ethical and metaphysical idealism belong as a rule to the outfit of the modernistic, liberal philosophy of religion (where in some form or other it is proclaimed as a fitting and saving interpretation of Christianity for the modern man), but so-called Christian realism is opposed to a substantial part of the heritage of liberal theology. It is from this perspective then that the work of Reinhold Niebuhr is to be judged, as is agreed by the majority of his biographers and as follows from his own formulations of his programme.