Toward the end of Nella Larsen’s Passing (1929), the protagonist Irene Redfield imagines how her friend Clare Kendry’s racist husband might react if he discovers his wife’s “true” racial identity: “What if Bellew should divorce Clare? Could he? There was the Rhinelander case.” This essay argues that what seems like a casual reference to a contemporary event actually underscores a central theme of the novel: the Rhinelander case and Passing both illustrate the problematic ways Americans sought to categorize mixed-race individuals in the 1920s, but while the Rhinelander verdict denies the existence of a middle ground between racial absolutes, the novel affirms it. Larsen directly references the Rhinelander case only once, but its themes echo throughout the text of Passing, which challenges the visibility of race and the conception of racial identity as intimately connected to one's essential self. Irene's reference calls to mind a very public trial that forced Americans to question their understanding of racial difference. In Passing, Larsen explores the conceptions of race as a real physical fact and as an imagined social construct, and challenges the logic of “common knowledge” and visibility in assigning racial identity to individuals.