 Given that quantum gravity does not yet exist as a working physical theory, one might legitimately question whether philosophers have any business being involved at this stage. Certainly the philosopher’s task will be somewhat different from that faced when dealing with a more-or-less settled body of theory such as classical Newtonian mechanics, general relativity, or quantum mechanics. In such cases, one typically proceeds by assuming the physical soundness of the theory or theoretical framework and drawing out the ontological and perhaps epistemological consequences of the theory, trying to understand what it is that the theory is telling us about the nature of space, time, matter, causation, and so on. Theories of quantum gravity, on the other hand, are bedeviled by a host of technical and conceptual problems, questions, and issues that make them largely unsuited to this kind of interpretive approach. In the case of string theory, there isn’t even really a ‘theory’ to speak of, so much as several clues pointing to what many hope will some day be an applicable, consistent physical theory. However, philosophers who have a taste for a broader and more open-ended form of inquiry will find much to think about, and it is entirely possible that future philosophers of physics will be faced with problems of a very different flavour as a result of the peculiar nature of quantum gravity. Indeed, Tian Cao argues that quantum gravity offers up a unique opportunity for philosophers of physics, leaving them “with a good chance to make some positive contributions, rather than just analysing philosophically what physicists have already established” (Cao, 2001, p. 138). This sentiment has in fact been echoed by several physicists, not least by Carlo Rovelli (a central architect of the approach known as loop quantum gravity), who complains that he wishes philosophers would not restrict themselves to “commenting and polishing the present fragmentary physical theories, but would take the risk of trying to look ahead” (Rovelli, 1997, p. 182). This raises an important point: though we think of general relativity and quantum theory as ‘nice’ theories from the point of view of philosophical investigation, in a very real sense they are not the whole story and break down at extreme scales. 