In this study of the rare twelfth-century treatise On Diverse Arts, Heidi C. Gearhart explores the unique system of values that guided artists of the High Middle Ages as they created their works. Written in northern Germany by a monk known only by the pseudonym Theophilus, On Diverse Arts is the only known complete tract on art to survive from the period. It contains three books, each with a richly religious prologue, describing the arts of painting, glass, and metalwork. Gearhart places this one-of-a-kind treatise in context alongside works by other monastic and literary thinkers of the time and presents a new reading of the text itself. Examining the earliest manuscripts, she reveals a carefully ordered, sophisticated work that aligns the making of art with the virtues of a spiritual life. On Diverse Arts, Gearhart shows, articulated a distinctly medieval theory of art that accounted for the entire process of production—from thought and preparation to the acquisition of material, the execution of work, the creation of form, and the practice of seeing. An important new perspective on one of the most significant texts in art history and the first study of its kind available in English, Theophilus and the Theory and Practice of Medieval Art provides fresh insight into the principles and values of medieval art making. Scholars of art history, medieval studies, and Christianity will find Gearhart’s book especially edifying and valuable.