The article seeks to retrace the processes by which Jewish converts and their descendants in the late medieval Kingdom of Naples were included into and/or excluded from Christian society. It focuses on a case study of the Apulian seaport of Trani. Following a systems theoretical perspective, it conceives exclusion as a multidimensional process of (re-)production of differences in social practices that affect the position and action of an individual in different fields of society. It then attempts to explain the success and failure of the inclusion of converted Jews and their descendants into Christian society by analysing the reproduction of difference as an interplay of cultural and material factors.