This book traces the history of male infant circumcision from its origins in ancient Judea, through centuries of Christian condemnation and Jewish defense, to its current role in American culture and medical practice. Genesis 17 is the biblical text where infant circumcision was mandated by Judean priests in the 6th century BCE; they characterized it as confirming a covenant, but the deeper meaning of the practice was male supremacy and dominance. Early Christians vehemently rejected circumcision, while Jews defended it with equal vigor in the Talmud and other rabbinic texts. The circumcision rite, embellished by folk practices and raised to new heights of significance by Jewish mystics, evolved into its contemporary form in medieval and early modern Europe. Meanwhile, Christian theological writings and medieval European folk beliefs — including those connected with fantasies about ritual murder — contributed to the enduring negative image of circumcision in the non-Jewish world. In the modern period, a few Jews began to question circumcision for the first time. In Germany, where Reform Judaism originated, German-Jewish physicians debated whether ritual circumcision should be either modified or eliminated. In the late 19th and 20th centuries, infant circumcision became a widely accepted medical practice in Britain and the United States, not as a ritual practice but as a preventive or therapeutic procedure. A key element in the new attitude to circumcision was the belief that the practice explained Jewish health and longevity. In the United States, Jewish physicians became especially prominent advocates for the practice, but physicians throughout the country endorsed it with equal enthusiasm. The contemporary circumcision debate in America finds expression in a wide variety of media: most notably, fiction, guides to Jewish parenting, and television sitcoms. The book closes with an epilogue assessing whether circumcision is beneficial or harmful, and whether parents have the right to request genital alteration for their infants or children.