This study is the first examination of Jesuit prison ministry in the Holy Roman Empire during the period of witch trials. It provides new insights into the prisons where the persons detained for witchcraft were incarcerated, as well as into their trials, including their torture and executions — as seen through Jesuit eyes. In this context, the Cautio Criminalis appeared, written by Friedrich Spee SJ (1591–1635), dealing with the question of the legality of these trials and the related prison ministry, and printed pseudonymously in 1631 and again in 1632. For the first time, the book offers a complete biography of Spee, who was nearly forced to leave the Society of Jesus; it outlines the book’s publication, and provides a detailed analysis of the Jesuit prison visits. The book also details Spee’s criticism of prison ministers, as well as his arguments about the guilt or innocence of the imprisoned, tortured and executed women and men of this tragic period in European history.