Gratian's Decretum, completed around 1140, represents a monumental development in the history of canon law and Christian political theory. As the foundational text for a new, systematic approach to Church law, Gratian’s work combined the ancient canons with innovative scholastic methods, reconciling contradictions and offering a cohesive legal framework. This Concordia discordantium canonum (Concordance of Discordant Canons) not only became the cornerstone for the study and practice of canon law but also influenced the broader legal and governmental systems of medieval Europe. The Decretum introduced methodological rigor reminiscent of Abelard's scholastic theology, creating a system for resolving conflicting canons through distinctions and contextual interpretations. Gratian's work was pivotal in shaping the legal culture of the Church, establishing him as the "father of the science of canon law." This study delves into the Decretum’s historical context, arguing that its significance extends beyond its intellectual contributions to include its engagement with the political and ecclesiastical dynamics of the mid-twelfth century. Gratian’s efforts coincided with critical developments in Church reform, the assertion of papal authority, and debates over the relationship between spiritual and secular powers. Far from being an isolated academic exercise, the Decretum reflects a deliberate attempt to create a Christian theory of societal structure and governance. By considering its original purpose and comparing it with contemporary works, this analysis positions the Decretum as a key document in understanding the interplay of law, theology, and politics in medieval Christendom. Through this lens, Gratian’s work emerges not only as a legal text but as a significant contribution to the theory and practice of ecclesiastical and political order. This title is part of UC Press's Voices Revived program, which commemorates University of California Press’s mission to seek out and cultivate the brightest minds and give them voice, reach, and impact. Drawing on a backlist dating to 1893, Voices Revived makes high-quality, peer-reviewed scholarship accessible once again using print-on-demand technology. This title was originally published in 1972.