The Thirty Years’ War (1618-1648) is notorious for levels of bloodshed and atrocity unprecedented in European history. The project Massacre and the Law: Atrocity, the Holy Roman Empire, and the Thirty Years’ War investigates how Catholic, Lutheran and Calvinist jurisprudents and moral theologians, military practitioners and political theorists responded to the reality of decades of excessive violence in war. The project aims to establish whether continual, direct and indirect exposure to military atrocity caused conceptual and discursive shifts in contemporary German thinking about ‘just war’ (ius ad bellum) and ‘just conduct in war’ (ius in bello). I work on a wide range of sources, predominantly in German and Latin, including legal and theological treatises, diaries, the correspondence of political and military leaders, and the records of military courts. Many victims and witnesses to excessive violence clearly struggled to reconcile their experience within existing norms. My time at the Herzog-August-Bibliothek is dedicated to authors who made personal experience of atrocity the cornerstone of their intellectual response to the problem of transgressive violence in war.