This dissertation offers a multi-dimensional picture of eucharistic devotion among the faithful of the Southern Low Countries in the thirteenth century. The method is to assemble writers of various genres in order to demonstrate that they shared a common theological framework for eucharistic devotion, which holds the triune God as the beginning and end. This framework presumes that life is a journey, with Christ as the way, and which is stabilised by the eucharist at its centre. In effect, the trinitarian context proves to be fundamental in all genres of eucharistic devotion from the strictly theological approach of the treatises of male scholastics and testimonies of mystical women through to the pastoral practice of ecclesial action, public ideals of sanctity, preaching, and liturgical practice. Chapter one offers a background into the theology of the Trinity and its relation to eucharistic theology in this period. The second chapter provides a detailed study of the visions recorded by the Brabantine mystic Hadewijch. Although experiential rather than speculative, her work reveals that a sophisticated understanding of the Trinity shaped her eucharistic devotion. Chapter three examines a range of works of the scholastic theologian Hugh of St. Cher. Hugh is an interesting case study from that genre of writers on account of his interaction with the local religious personalities in Liége and his service to the campaign for Corpus Christi. The texts included in this chapter complement the abstractly theological perspective with the practice of preaching, a commentary on the mass, and Hugh's action as an ecclesiastical statesman. Chapter four follows naturally from Hugh's involvement in Liége by exploring the devotional life of Juliana of Cornillon and Ida of Nivelles through their vitae. These texts present an ideal of sanctity and devotion that places ritual practices involving the eucharist squarely in the context of devotion to the Trinity. Concerning the feast dedicated to the eucharist, Juliana herself explained that it always existed in the secret of the Trinity, semper fuit in secreto trinitatis.