Clandestine marriage—the medieval institution of Christian marriage undertaken outside the recognition of legal authorities—was increasingly the object of anxiety and renegotiation in the early modern world. Its illicitness undermined marriage as a managed exogamy, posing a threat not only to social controls but also to familial expectations and honor. This threat provides the central tension of the story of the Duchess of Amalfi, a tale—about a noble widow who secretly weds her steward to avoid public censure—that was adapted across early modern Europe. Focusing on analogous Spanish and English dramatic retellings of this story by Lope de Vega (1562–1635) and John Webster (ca. 1580–ca. 1634), respectively, this essay explores the tale's transnational participation in prevalent sixteenth-and seventeenth-century debates about the dangers of clandestine marriage embodied by the threatening figure of the widow. By showing that many apparent differences between adaptations of this tale can be explained with reference to their distinct, but related, concerns with clandestine marriage, this article demonstrates the centrality of legal questions to transnational literary adaptation.