The development of medical drug therapy in medieval times can be seen as an interplay between tradition and innovation. This book follows the changes in the therapy from the Arabic medicine of Ibn Sīnā (Avicenna) to Latin medical scholasticism, aiming to trace both the continuity and the development in the theory and practice of medieval drug therapy. In this delicate balance between change and continuity a crucial role was played by the scientific community through critical rejection or acceptance of new ideas. The drug choices were in most cases rational also from the point of view of contemporary medical theory. The method used in the book for studying these choices could promote the development of a novel methodology for historical ethnopharmacology.