In the late seventeenth century, reports of vampire attacks began to emerge out of eastern Europe. These stories became the focus of a scholarly debate that centered on whether the events described in the vampire reports could possibly be true and, if so, how they ought to be explained. The reports presented a dilemma: although the events they described were implausible, the reports were often supported by testimony from reliable sources. This article will explore two eighteenth-century interventions in the vampire debate, and consider how they responded to this tension. Augustin Calmet carefully documented and examined the vampire reports, using established natural philosophical models for the study of strange phenomena. Despite Calmet's rational methods and skeptical conclusions, his work on vampires was vociferously attacked by Voltaire. I will argue that the encounter between Calmet and Voltaire illustrates their different ways of understanding the relationship among superstition, knowledge-production, and testimony.