"Loving the Neighbor" assesses the ethics of difference in the shared romance narratives of late medieval England and Castile (1360-1450). It appraises the ethics informing portrayals of community across differences of religion, race, gender, and history. To this end, "Loving the Neighbor" analyzes late-medieval English and Castilian romances as they engage the Judeo-Christian ethical demand to love the neighbor as the self. Weaving together familiar and understudied geographies, languages, and texts, it analyzes desire and aggression as attributes of neighbor relations. Via the theoretical category of the neighbor, the dissertation argues that fantasies of difference, such as the Saracen and Jew, function to illuminate medieval Christians' anxieties over their ethical injunction to love their neighbors as themselves. The Castilian context is especially relevant to this work, given a centuries-long medieval history of convivencia (living together): the flourishing of Judaism and Islam alongside, but also in conflict and competition with, Christianity. This project delves into both the historical archive and contemporary psychoanalytic theory to assess the oscillating fantasies of mutual regard, reluctant acceptance, and violent aggression among Christian, Saracen, and Jew in late-medieval romance, and to broaden our understanding of ethical dilemmas pervasive in late-medieval literatures.