 Our interest in natural kinds is generated by the fact that the particular sciences make frequent use of what, on the face of it, seem to be natural kinds. So an important question is whether the kinds of the special sciences (e.g. psychology, economics, biology, chemistry and so on) do in fact satisfy the conditions laid out by metaphysicians for natural-kindhood (Fodor 1974; Dupré 1981, 1993; Millikan 1999; Ellis 2001). And to the extent that they do not, does that show that these kinds are not genuine natural kinds after all, but are something different? Or does it show that the metaphysicians need to revise their theories of natural kindhood? The metaphysical issues raised by the special sciences vary. For example, philosophers of biology ask whether species would be better understood as being individuals rather than natural kinds. The so-called species problem (Ghiselin 1974, 1987, 1997; Hull 1976, 1978; Kitts and Kitts 1979, LaPorte 1994) asks which are the appropriate criteria to use in order to decide which particular species an organism belongs to. This is particularly challenging because species evolve over time, which makes it difficult to determine when we should recognize a new species and distinguish it from a distinct, older ancestor species or from distinct sister species. Furthermore, the criteria advanced by most of the various species concepts on offer involve relational rather than intrinsic properties of organisms. So either species are not natural kinds or the view that kindhood is fixed by the intrinsic properties of things must be revised. In the philosophy of chemistry, a key question is whether chemical kinds provide as much support for microstructuralism as the stock examples discussed by metaphysicians suggest (Hendry 2006; LaPorte 2004; Needham, 2000, 2002; Van Brakel, 2000). Microstructuralism is the view that chemical kinds can be individuated solely in terms of their chemical microstructure. Chemical elements would appear to support microstructuralism since atomic number is sufficient to individuate any element. However, the extension of this view to more complex chemical structures (such as molecules) is much discussed in the literature. In the philosophy of mind, the ontological status of psychological kinds has been questioned in the light of modern advances in neuroscience (Churchland 1981; Fodor 1974). In particular, action is causally overdetermined by mental and neurophysiological kinds. If neuroscience can provide a sufficient account of action, then the role of our common-sense folk psychological concepts, such as belief and desire is called into question. Maybe there are no psychological natural kinds corresponding to those concepts. Natural kind realists reject the conventionalist view that in all cases the boundaries of ‘natural’ kinds are drawn by human interests. But is it plausible to draw a distinction between genuinely natural and conventional kinds when it comes to the social sciences? In particular, is it important that, via a feedback effect, human perceptions of what kinds there are can have an effect on the composition and even existence of those kinds (Hacking 1995)?