The writing of this book was inspired by a two-fold correspondence with a priest friend. The two issues that he raised were: first, the decision by the Vatican to recognize as both valid and licit the use of that version of the Anaphora1 of Addai and Mari which has no obvious "words of consecration"; and second, my description of the term "Transubstantiation" as contentious. I had not written anything focussed on the doctrine of the Eucharist previously, because I believed that this topic has been covered very thoroughly by many other writers of greater scholarship than myself. However, it now seems to me that I do have something worthwhile to contribute to the topic. This book covers the theology, philosophy and spirituality of the Eucharist. I believe that it is impossible to separate these from another without doing violence to one's appreciation of and participation in the Eucharist. The structure of the book is as follows. I begin with a review of the Scriptural texts pertinent to the Eucharist and propose a novel theory regarding its institution. I then consider a variety of Patristic texts which are advanced by Roman Catholic, Byzantine Orthodox and Protestant disputants as favouring their particular Eucharistic theologies. Next, I present a theological analysis of the Eucharist as the three-fold rational sacrifice which fulfils the Aaronic worship ritual. I then discuss the controversy over the "form of the Eucharist" before discussing Eucharistic Ontology from a Platonist perspective. Finally, I discuss Eucharistic spirituality and critique the revolutionary changes made to the Roman Liturgy in the name of pope Paul VI.