This dissertation from the University of Würzburg stakes out some carefully defined territory in the crowded field of heresy and inquisitorial studies. It does so by returning to some of the most frequently studied sources in this field: the early handbooks through which papal inquisitors established the legal and procedural framework of their new (in the thirteenth century) office. Scholars of inquisition going back to Célestin Douais and Henry Charles Lea in the nineteenth century, and indeed as far back as Franciscus Pegna in the sixteenth century, have worked with these texts. Bivolarov, however, identifies an area that he finds has not received systematic study: namely, the papal decrees and legal opinions of trained jurists on which thirteenth-century inquisitors relied when compiling their handbooks.