During the past two decades, historians have been brought into legal cases in unprecedented numbers. As the courts have tried to adjudicate responsibility for environmental and occupational diseases, history and historians have played an increasingly central role in shaping decisions in the cases themselves as well as in related social policy. In suits over tobacco-related diseases, asbestosis, harm from radiation, and other toxic substances, historians of technology and science, social history, and public health are being brought to the courts in growing numbers to provide expert testimony aimed at assessing responsibility for damages that have arisen years, sometimes decades, after exposure. As the role of the historian has expanded, so, too, has the controversy surrounding the participation of historians in legal cases. In this essay, the authors have gone through their own internal process in deciding whether to work for those injured by industries, institutions, or products. The authors share their experience when they became expert witnesses in two cases. Their experience and the controversies that are roiling the historical community take on a special resonance in the light of the recent BP disaster in the Gulf of Mexico.