In 1598, the year that Duke Cesare d’Este (1562–1628) lost Ferrara to papal forces and moved the capital of his duchy to Modena, the papal Inquisition in Modena was elevated from vicariate to full inquisitorial status. Despite initial clashes with the duke, the tribunal began not only to prosecute heretics and blasphemers, but also professing Jews. Such a policy towards infidels by an organization appointed to inquire into heresy (inquisitio haereticae pravitatis) seems unusual. How did the papal Inquisition come to assume authority and prosecute Jews in early modern Italy? Examination of trial procedure of Jews as opposed to that of Christians will help decide if there is anything distinctive about the Holy Office’s treatment of Jews. It will be argued that inquisitorial tribunals were disarming the Jewish threat to Christian society, not for its own sake, but as an attempt to impose social and religious discipline on the Christian community.