The double treatise "On the Holy Mass" and "On the Body of the Lord," which has been regarded as a work of Albert the Great (1200-1280) since its inception and has enjoyed widespread distribution, is one of the finest testimonies to Eucharistic piety and theology of the Middle Ages. The first book explains the Mass celebration from the Introit to the dismissal, including a detailed commentary on individual rites and prayers, such as the Gloria, the Credo, and the Eucharistic Prayer. The subsequent second book presents the sacrament of the altar under its various designations: as gift and offering, as sacrifice, food and drink, as communion and sacrament of the Church. Written by a great theologian and experienced pastor who has thoughtfully contemplated the liturgy in prayer, this work can still guide readers today to a deeper understanding of the "most precious gift" and to a vibrant participation in the Eucharistic service.