In 1398, the faculty of theology of the University of Paris condemned 28 articles pertaining to ‘magic arts’, ‘sorceries’, and ‘similar superstitions’. The theologians left no doubt about the threat they felt such ‘nefarious, pestiferous, and monstrous abomination’ presented to Christian society. They also stressed, however, that ‘it is not our intention in any way to disparage licit and true traditions, science, or arts, but we will try to uproot and extirpate, insofar as we are able, the insane and sacrilegious errors of the foolish and the deadly rites that harm, contaminate, and infect orthodox faith and Christian religion’.1 This was a necessary qualification because, as threatening and harmful as superstitious rites were understood to be, they frequently bordered on practices that were legitimate, respectable, and in some cases even revered. The boundaries between licit and illicit acts could be very difficult to discern, even for highly educated experts. Medieval authorities did not need to debate whether superstition ought to be condemned, because for them the term superstitio always denoted a condemnable error. The troubling issue was instead what sort of practices were to be understood as superstitious. This chapter will address this question, examining how the medieval church defined superstition, surveying the kinds of practices, both common and elite, that could fall within this broad category, and outlining how levels of concern heightened over time.