The doctrine of the ‘double Procession’ of the Holy Spirit, in spite of all the controversy it has caused in the past, is today probably regarded as one of the more trivial elements in our Western theological heritage—slightly more important perhaps than the conclusions reached in the medieval arguments over the number of angels who could stand on the point of a pin, but still of no great intrinsic significance. Yet this doctrine was a major factor in the schism between East and West, and it has since then remained an obstacle to all attempts to reconcile the Eastern and Western Churches. Western theologians have clearly felt that something of importance was being affirmed in the ‘Filioque’ clause in the Nicene Creed, while their Eastern counterparts have been equally convinced that what the ‘Filioque’ affirms is wrong, even blasphemous. The questions of what it is that the ‘Filioque’ is intended to affirm, and of whether what is affirmed should be affirmed, are therefore of some importance, particularly in an age of ecumenical dialogue. On these grounds alone, the doctrine demands to be seriously examined: we are not entitled simply to ignore it, or—what is worse—to cast around for superficial reasons for getting rid of it in the hope of thereby reaching an agreement with Eastern theologians.