Canon law scholarship flourished in the twelfth and thirteenth centuries, and its practitioners left a remarkable paper trail. Surviving documents capture the intellectual evolution that occurred during this formative period and offer historians a rare opportunity to trace legal development in premodern times. This article examines the evolution of laws regulating the sharing of meals with non-Christians, with particular attention to the ways in which medieval canonists conceptualized foreigners. These canonists struggle to fit Islam into traditional legal categories, concluding that Muslims are “judaizing pagans” on account of their dietary practices. This outcome, and its implications for the way canonists understood not only commensality with Muslims but also with Jews and pagans, reflects the degree to which medieval scholars of canon law were both unfamiliar with other religious traditions and uninterested in acquiring such knowledge. The ideas of these scholars about non-Christians reflect their detachment from realia and their commitment, as participants in the canon law tradition, to the conservation of existing paradigms, laws, and interpretations. This case study thus sheds light both on medieval Christian conceptions of foreigners and on the ways in which great works of premodern law developed.