In this groundbreaking essay, Michael L. Cook addresses two major Christological concerns. First, Cook discusses how Christology must be Trinitarian insofar as it addresses and advocates a more active role of the Holy Spirit as a person. This includes both the economic activity of the triune life in creation and the dynamic, perichoretic, interactive life of God as God. Second, he examines how Christology must be ecumenical insofar as it addresses the concerns of both East and West with regard to the filioque. While it is important ecumenically to return to the original Creed of 381, the theological issues that have developed over the centuries cannot be ignored. The question finally is whether East and West can come to a convergence of views. Thus Cook sets the Eastern views of Vladimir Lossky and John Zizioulas in dialogue with three Western approaches—Jürgen Moltmann, David Coffey, and Thomas Weinandy—that seek creatively to develop insights potentially compatible with the Eastern viewpoint. The aim is to promote ecumenical dialogue that can transcend the differences occasioned by the filioque, and to seek a higher ecumenical unity based in a renewed emphasis on the Holy Spirit’s activity.