William of Saint-Thierry, Isaac of Stella, and Baldwin of Forde created a distinctly Cistercian body of Eucharistic theology in the twelfth century. In this book, Nathaniel Peters offers a scholarly account of that theology and examines the connection between medieval Trinitarian and Eucharistic theology. These Cistercian authors thought that the character of God as a Trinity of persons united in essence provides the structure of the economy of salvation—especially its turning point, the Eucharist. They saw the Eucharist as the place where the ontological union of the Incarnation becomes intimate, personal, and communal. In the Eucharist, God the Father draws those who receive to himself by uniting them to the body and blood of the Son. This unity brings an increase of unity with the Holy Spirit. Once united to the Son and Spirit, the faithful are united to the Father. The Eucharist also connects the meditation, sacrifices, and offering of their own lives to the life of Christ, with which they are offered to the Father. Chapter 1 examines the thought of William of Saint-Thierry, who has the most developed understanding of Eucharistic presence, conversion, and reception. It also treats the connections William draws between Eucharistic reception and meditation on scripture and the passion of Christ. Chapter 2 treats Isaac of Stella, who uses more intellectualist imagery and imagery of the mystical body of Christ. Chapter 3 studies Baldwin of Forde, who argues that the term transubstantiation best describes Eucharistic conversion and emphasizes reception by faith in the truth about Christ. Chapter 5 offers a brief conclusion, with reference to later thinkers who explore the Trinitarian shape of the Eucharist in similar ways.