Are artefacts, that is, human-made objects, distinct from the natural things that they are made out of? For example, is a chair a thing distinct from the pieces of wood used in making it? This question is intensely debated in contemporary metaphysics, but it is little known that there was an equally heated and sophisticated debate concerning this issue in the late Middle Ages. This book provides the first comprehensive reconstruction, analysis, and evaluation of this discussion, looking at both the most famous figures such as William of Ockham as well as dozens of previously unstudied texts available in manuscript form only.