Much of this collection of articles [on Byzantine medical books] concerns medical texts that seem eminently ‘practical’ or ‘useful’. 1 But what does either of those adjectives mean? How can historians of medieval Greek medicine, usually working on writings that now lack contextual evidence of origins and application, establish criteria of usefulness or practicality? Those who study medical remedies of the pre-modern period are often asked – by ‘lay’, non-specialist audiences in particular – ‘Did they work?’ The question usually presupposes a certain kind of effectiveness as the yardstick: that of modern, laboratory-based biomedicine with its high levels of pain relief – on which yardstick medieval remedies generally fall short, proving neutral at best. 2 In the same way, the question put (in effect) to scholars of medieval medical manuscripts – ‘Were they used?’ – presupposes a certain vision of the texts’ Sitz im Leben as providing the sole criterion. 3 In effect, if the text did not sit in the consulting room, and if it was not frequently in the doctor’s hand, at least between patients and perhaps during a consultation, it was not or useful. What follows is a short statement of the obvious contrary position. Just as there are many kinds of effect and effectiveness that can be ascribed to remedies, 4 so there are many kinds of usefulness with respect to medical texts. In each case we need to separate out the different kinds to arrive at a suitable typology, and we need to try to arrive at criteria for each kind – ideally, in the case of texts, related to aspects of the manuscripts in which we find them.