This book uncovers a startling medieval fantasy: the belief that Jewish men menstruated. From the twelfth to the seventeenth century, Christian writers imagined the Jewish male body as leaky, feminized, and dangerously deviant. The figure emerged across theology, medicine, and polemic as a powerful symbol of disorder, collapsing boundaries between male and female, sacred and profane, Christian and Jew. Far from a marginal oddity, the menstruating Jew shaped Christian ideas of bodily normativity, religious difference, and moral hierarchy. Bringing together queer theory, historical scholarship, and close textual analysis, this book argues that this grotesque fantasy was not merely about antisemitism, but about managing deep fears surrounding gender, sexuality, and identity. In reframing how medieval Christians imagined Others, it offers a bold new contribution to the histories of religion, embodiment, and queerness.