This study explores the treaties signed between European states and the Islamic Maghreb in the Middle Ages, the role these agreements had in defining the states’ domains, and the supervision and control they imposed on European merchants in Islamic ports. At the time, these treaties fulfilled a host of diplomatic, security, and economic functions that regulated relations between the contracting states. Al-Mansuri discusses the regulation of the foreign merchants’ freedom of movement, and notes how the ports of call were determined prior to the permitting of foreign trade, and how such arrangements went beyond the physical equipment necessary to include hospitality and customs services. This permitted the host countries to regulate and supervise the merchants’ activities, which were specified in the treaties and spoke of the necessity to provide security for merchants and their assets. The treaties also specified where the merchants were allowed to stay while anchored in the harbor. At a time when Mediterranean states viewed people of other nationalities with suspicion, the use of inns allowed close supervision of foreign merchants. Throughout this study, al-Mansuri addresses a field long neglected by Arab scholars.