It is still sometimes maintained that the doctrine of the Holy Trinity is a baffling puzzle of no relevance to the Christian life. The history of the last century of theological reflection hardly supports this: from Karl Barth onwards (and if we look further East, for much longer), the doctrine of the Trinity has been reclaimed as a fundamental tenet of Christian doctrine. Nevertheless, this volume of collected essays seems to think that the case needs to be made again: the Holy Trinity does not just exist in the minds of abstruse theologians but is deeply bound up with the life of the Church. The essays in this volume, based on the proceedings of a conference held in 2008, are divided into three parts: ‘The Trinity in Christian Worship’; ‘Jesus Christ, the Trinity and Christian Salvation’; and ‘The Trinity and Ecclesial Being’. The first part is particularly important, for one matter neglected in older studies on the doctrine of the Trinity is how the doctrine is rooted in Christian prayer and worship; to see it as a piece of celestial (or supercelestial) metaphysics is a fundamental misunderstanding. The mere fact that this section stands first speaks volumes for the approach adopted here. Part ii contains a collection of historical studies: pride of place must go to Brian Daley's account of the Trinity in Maximus the Confessor and John Damascene, recognising the importance of the Trinity in theologians usually regarded as primarily concerned with Christology, and presenting their sometimes intricate thought with grace and clarity. The final part concerns the Trinity in relation to the Church. John Behr's paper on the Trinitarian being of the Church is, in fact, a critique of the line taken by many Orthodox theologians of the last half century who have been seduced by a deceptive parallelism between the unity of the Persons of the Godhead and the unity of Christians in the Church. Behr suggests that we need to discern the relevance of the Trinity to the Church by thinking of the Church as the People of God (the Father), the Body of Christ, and the Temple of the Spirit: thinking like this roots our understanding of the Church in God's Trinitarian activity in the world. Kathleen McVey seeks to open up questions of gender by appealing to the Syriac tradition and in particular to Ephrem. Her conclusions are modest, but all the more effective for that. The final conclusion is left to Brian Daley, who draws out from a variety of sources, patristic and Jesuit, a profoundly Trinitarian understanding of what is involved in following Christ. No one reading this volume could imagine that the doctrine of the Trinity is irrelevant to the life of the Christian; one might, however, wonder why they seem to protest so (too?) much.