Gratian the Theologian shows how one of the best-known canonists of the medieval period was also an accomplished theologian. Well into the twelfth century, compilations of Church law often dealt with theological issues. Gratian's Concordia discordantium canonum or Decretum, which was originally compiled around 1140, was no exception, and so Wei claims in this provocative book. The Decretum is the fundamental canon law work of the twelfth century, which served as both the standard textbook of canon law in the medieval schools and an authoritative law book in ecclesiastical and secular courts. Yet theology features prominently throughout the Decretum, both for its own sake and for its connection to canon law and canonistic jurisprudence.