Thesis advisor: Boyd T. Coolman / William of Saint-Thierry, Isaac of Stella, and Baldwin of Forde created a distinctly Cistercian body of Eucharistic theology in the twelfth century. But despite one article that examines none of the Eucharistic treatises and omits Isaac and Baldwin, there is no scholarly account of Cistercian Eucharistic theology. Nor is there more generally a historical work that examines the connection between medieval Trinitarian and Eucharistic theology. This dissertation seeks to fill both lacunae. The introduction of the dissertation sets the historical and scholarly context for investigation. 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 describe Eucharistic conversion. Baldwin emphasizes reception by faith in the truth about Christ. Chapter 5 offers a brief conclusion. These Cistercian authors thought that the character of God as a Trinity of persons united in essence provides the form or structure of the economy of salvation—especially its turning point or climax, the Eucharist. This emphasis on Trintiarian dimensions is the hallmark of Cistercian Eucharistic theology. They saw the Eucharist as an analogue to the Incarnation, a site where the economic missions of the Trinity take place. 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 and to the unity that all three persons share. The Eucharist is, then, not only a site of God’s movement toward human beings, but of human movement back toward God. It acts as a kind of pivot point in the economy of salvation: the moment where the outpouring of the Son and Spirit join most deeply with the faithful and draw them back to the Father. The Eucharist also binds the members of the Church, the body of Christ, to each other and to their Head in his act of self-offering to the Father. It connects the meditation, sacrifices, and offering of their own lives to that of Christ, with which they are offered to the Father.