Custom was fundamental to medieval legal practice. Whether in a property dispute or a trial for murder, the aggrieved and accused would go to lay court where cases were resolved according to custom. What custom meant, however, went through a radical shift in the medieval period. Between the twelfth and thirteenth centuries, custom went from being a largely oral and performed practice to one that was also conceptualized in writing. Based on French lawbooks known as coutumiers, Ada Maria Kuskowski traces the repercussions this transformation – in the form of custom from unwritten to written and in the language of law from elite Latin to common vernacular – had on the cultural world of law. Vernacular Law offers a new understanding of the formation of a new field of knowledge: authors combined ideas, experience and critical thought to write lawbooks that made disparate customs into the field known as customary law.

‘This book is a marvel, mixing erudition and imagination. Describing the cultural upheaval of the writing of custom, Ada Kuskowski opens new doors to the understanding of medieval law.’

James Q. Whitman - Yale Law School

‘In the first comprehensive study of the earliest Northern French lawbooks known as coutumiers, influential myths about the rules and procedures of lay courts known as customary law are met with challenging scrutiny. Kuskowski compellingly argues that, with no prototype available, the coutumier authors imaginatively shaped a new form of learned and official law for lay jurisdiction and for a new audience of regional secular elites. Coutumiers were the paradigm-shifting achievement of expert legal minds who, in creating an idiom to think with and about custom, profoundly affected medieval legal culture.’

Brigitte M. Bedos-Rezak - New York University

‘This study is a revelation. Early French customary law emerges from it as the dynamic creation of sophisticated juridical thinkers, who worked not to record local traditions, but to shape and teach a distinct form of legal practice and thinking for secular courts across thirteenth-century France. By studying the first coutumiers as a coherent whole, with a focus on language and manuscripts and an eye toward recent scholarship in legal history generally, Kuskowski defines a subject every bit as complex, interesting, and influential as the medieval Roman and canon laws that overshadow it in the historiography.’

Adam Kosto - Columbia University