The revival of interest in Trinitarian theology, beginning in the 1980s with works such as Jürgen Moltmann's The Trinity and the Kingdom of God and John Zizioulas's Being as Communion, led to a widespread assumption that Western Christianity had effectively given up on a Trinitarian doctrine of God some centuries ago. This timely and important book demonstrates that, at least so far as the Wesleyan tradition is concerned, this is an oversimplification. Its author serves as professor of systematic theology and Stanley Professor of Wesley Studies at The University of Dubuque Theological Seminary and is particularly known for his exposition of the Trinitarian theology of Thomas Torrance. In this work he focuses on his own Methodist tradition, arguing that a vision of ‘participation in the economic trinity’ is a neglected yet central aspect of John Wesley's theology. In doing so he combines detailed historical research with passionate advocacy.The first chapter takes the reader to the Trinitarian controversies in seventeenth- and eighteenth-century English theology. This gives a valuable summary of arguments from the various disputants who either criticized the doctrine as unbiblical and/or unreasonable or defended it on the basis of a (usually outdated) philosophical framework. Wesley, says Colyer, needs to be read against the background of this theological controversy and, in particular, against the tendency for both opponents and defenders of the doctrine to divorce it from the worship and practice of Christian living: what Wesley called ‘vital religion’. The chapter ends with an exposition of Wesley's 1775 sermon ‘On the Trinity’, written at the request of the Methodist society in Cork. Wesley, argues Colyer, reunites what the Trinitarian controversy had driven apart: doctrine and life, belief and worship, the nature of God and human relations with God. Wesley's Trinitarianism, he concludes, is evangelical, doxological, and participatory.The remainder of the book seeks to justify this conclusion through a comprehensive search of Wesley's sermons and other published works and then to develop a Wesleyan vision of the church as ‘Trinitarian embodiment’. This involves taking issue with Wesleyan scholars such as Randy Maddox and Kenneth Collins, criticizing them for failing to appreciate the extent to which Trinitarian participation is such a dominant thread in Wesley's preaching and writing, providing what amounts to an organizing principle, or a lens through which the early Methodist movement can best be viewed. This theme of Trinitarian participation, says Colyer, crops up repeatedly in Wesley's preaching and animates his understanding of the church, not simply as a functional institution, but as the means by which we are incorporated into the life of God as the body of Christ. More than that: the forms of ecclesial practice developed in early Methodism (society, class, band, and so on) were practical expressions of a Trinitarian faith that was evangelical, doxological, and participatory.Two questions need to be asked of a book of this kind. The first is: Does the argument work? My answer would be by and large, yes. It may sometimes be overstated; I suspect Wesley was not quite as consistent or as theologically coherent as Colyer would like him to be. Nevertheless, he has given us a meticulously researched monograph that makes a significant contribution to the literature of Wesleyan theology. Incidentally, it was sometimes irritating to have to break off from the main text to follow a long argument that continued in the footnotes, an indication, perhaps, that the editors were unsure how much scholarship readers would cope with.But, granted that the picture painted here is historically well-founded, why might it be significant for the church of the present? It is a strength of Colyer's work that he sees historical theology as a servant of contemporary Christian life. Wesley's participatory Trinitarianism can help liberate us from the individualism that has plagued evangelical Christianity, giving us a vision of the Christian life that is necessarily communal because it involves participation in the communal economy of God. In addition, argues Colyer, this Trinitarian ecclesiology can help to correct that theologically inadequate and spiritually unhealthy understanding of the relation of the divine law to the person of Christ, which Wesley bequeathed to his successors. A vision of the Christian life that is more communal and less legalistic would be a very good outcome for this fine piece of theological investigation.