Gideon Libson’s highly original work on custom is the first attempt to present a comprehensive comparative study of Jewish–Islamic law on a particular topic during the early Middle Ages. His in-depth study of Islamic law—its sources, legal schools, and extensive legal literature—together with his expertise in the wide range of geonic and rabbinic literature enable him to determine the influence of Muslim practice on geonic custom.
In both systems of law the growth of custom was a reaction to the general culture. He shows conclusively how custom in both systems of law served as a conduit for the absorption of changes, thus helping to bridge the gap between the authoritative legal systems and the practical realities of the environment. Libson’s contribution to the study of comparative Jewish and Islamic law during the geonic period will be of value to scholars engaged in the study of comparative law.