This study shows how the trinitarian theology of Hans Urs von Balthasar opens up an aproach to the controverted question of God's immutability and impassibility which succeeds in respecting both the transcendence and the immanence of God. Contrary to both Process thought and the classical Thomist position, von Balthasar's scattered treatment is here presented thematically, in a way which makes it clear that his idea of an analogous event in the trinitarian God (in which we participate) is a radical reinterpretation of the traditional Christian axiom of divine immutability. In the course of outlining the distinctiveness of von Balthasar's approach, O'Hanlon introduces the reader to some of the fundamental themes of one of the major Roman Catholic theologians of this century, who is still relatively unknown in the English-speaking world.