This book centres around a critical edition and annotated English translation of an Arabic medical writing: On the Errors of the Physicians in Damascus, composed by the Jewish philosopher, Jacob ben Isaac (fl. AD 1202). The edition and translation are framed by a bio-bibliographical sketch of the author, a source-critical study of the text, a detailed description of the extant manuscripts, and various indices which make the material accessible from different angles. Jacob's treatise is significant in several ways: first, as an example for the lasting influence of the Greek medico-philosophical tradition, especially Galenism, on medieval Arabic and Jewish scholarship; second, as an authentic witness to the theoretical and practical state of Arabic medicine in the High Middle Ages; third, it illustrates the Jewish contribution to medieval Islamic science; and fourth, it contains valuable information relating to socio-cultural history in general.