It is well known that John Calvin's understanding of the mystery of the Trinity stressed that in his relation to the Father the Son is autotheos. That is, Christ's divine essence was not derived from, or generated by or communicated by the divine essence of the Father. ‘[W]e say that deity in an absolute sense exists of itself; whence likewise we confess that the Son since he is God, exists of himself, but not in respect of his Person; indeed since he is the Son, we say that he exists from the Father’ (Institutes i.13.25). The Son may derive his person from the Father, but not his deity; likewise the Spirit his person, as he proceeds from the Father and the Son, but not his deity. (How could they? They are divine in the fullest sense.) Yet Calvin was assailed from left and right, by the ‘Italian anti-Trinitarians’ in Geneva, such as Valentine Gentile, and by Trinitarians such as his fellow-countryman Pierre Caroli. One merit of Brannon Ellis's book is that it takes us through these various controversies in some detail for the first time. Indeed he does this tour more than once. First, in summary form from the text of the 1559 Institutes into which Calvin incorporated some of his responses to his assailants. Then in the bulk of the book the ground is traversed in more detail, including a discussion of the traditionally orthodox of the Reformed, for after his death Calvin's outlook came to be a ‘minority report’ in Reformed theology (chs ii–vi). (Perhaps the mainstream believed that they had controversies enough on their hands, without adding Trinitarianism to them, in which they [including Calvin] had no stake other than to be orthodox and ‘catholic’.) Ellis has much to say about Bellarmine, Arminius and the Remonstrants, the Cartesian Reformed theologian Herman Röell, and later Reformed Orthodoxy – Voetius and De Moor, Zanchius and Lucas Trecaltius Jr, Keckermann and Maccovius. Throughout these chapters another theme is developed, that of a ‘ruled Trinitarian language and its grammar’, to which the author gives more attention in the final chapter, along with some rather opaque discussion of modern Calvinian covenant theology. I think ruled language involves, in speech about the Trinity, always being clear what one is talking about: is it the one God? (In which case certain questions are pertinent.) Or is it the tri-personhood, or one of the persons ‘ordered’ in relation to the others? (In which certain different issues and ways of speaking are permissible.) And woe betide the speaker who does not know what he is talking about! The author's claim is that Calvin's autothean emphasis purifies such grammar, so making a significant contribution to Trinitarian theology. This erudite book will be of considerable interest to students of Reformed theology and (to a lesser extent) of Trinitarian theology more generally.