To write on the Trinity is to enter a minefield of presuppositions-presuppositions of theology, exegesis, grammar, logic, philosophy, etc. However, at the heart of Godʹs self-revelation in the Bible is God's tri-unity, that God is three, Father, Son, and Holy Spirit. Confessional Christians would identify this claim, that God is Triune, as a necessary condition of true Christian faith. To be Christian is to follow Christ who is the 2nd person of the Trinity. Yet, does following this Christ mean following the 2nd hypostasis who is eternally begotten of the Father, sharing with him his ousia? That is a more difficult question, isn't it? Indeed, many faithful men and women in my life could not make heads or tails of the latter claim while worshipping and following the Christ of the former. So, what does it mean to be Trinitarian? This book is about that question, what does it mean to be a Christian who worships a triune God, to be ʺTrinitarianʺ? Is the Trinity a doctrine, arrived at through second-order reflection on the Biblical data several hundred years after the canon closed, or is it something else? Is it, perhaps, a presupposition about the reality of God that has shaped the Christain imagination, that has shaped the framework Christians bring to the world, throughout created history?