In most modern historical surveys of medieval Islamic law, Twelver jurisprudence has been generally noted only where it intersected with what is assumed to be mainstream or normative Islamic law, i.e. Sunnī fiqh. Nonetheless, some modern scholars have briefly noted and occasionally commented upon the distinct phenomenon of major Twelver scholars crossing supposed sectarian lines to participate in and contribute to Shāfiʿite learning circles. This study analyzes the elements of legal borrowing and exchange between Twelver and Shāfiʿite jurists through a legal genre known as “adab al-qāḍī,” or “The Judge’s Protocol,” which has been mined by modern scholars as sources for laws of procedure. However, this overwhelming focus on the elements of practical law and the genre’s concerns for evidentiary standards and burdens of proof has overlooked the sophisticated discussions found in these texts regarding the processes by which judges come to a ḥukm, or ruling. This study undertakes an analytic comparison of Twelver Shīʿī adab al-qāḍī texts from the 11th to 14th centuries CE with a contemporaneous Shāfiʿite commentary tradition on al-Shāfiʿī’s al-Umm, the earliest extant adab al-qāḍī text. While Twelver and Shāfiʿite jurists shared many judicial concerns in adab al-qāḍī texts, their respective theological commitments and understandings of valid sources of authority accounted for some distinct approaches to questions of evidence, court procedure, and the judge’s legal reasoning, most salient of which was the Twelvers’ discussion of al-ḥukm bi ’l-ʿilm—the judge’s personal knowledge—and Shāfiʿite jurists’ emphasis on the tension between the judge’s ijtihād and madhhab cohesion. By undertaking an analysis of both Sunnī and Shīʿī jurisprudential texts in a discussion of adab al-qāḍī, this study argues against a reliance on solely Sunnī texts in an academic analysis of an Islamic legal genre. It also argues for the value of such integrative analysis in highlighting salient changes and developments within the adab al-qāḍī texts of both the contemporary Shāfiʿite and Twelver Shīʿī lineages, as well as the ways in which these jurists engaged with each other’s legal discourse.