John Fine's major re-interpretation of the history and nature of the medieval Bosnian Church and heresy has been long out-of-print and has yet to be superseded. Based on a wide-ranging and critical use of extant primary sources, he successfully challenges enduring stereotypes and presumptions about the religious and political history of medieval Bosnia which were formulated in nationalist, Slavophile and clerically-motivated reconstructions of Bosnian history in the late nineteenth and early twentieth century. This crucial work has far-reaching implications for an understanding of the complex religious history of medieval Bosnia and the process of its Islamization in the early Ottoman period which have attracted many controversies and conflicting theories.