Most philosophical theories of natural kinds fail to reflect successful classificatory practice in science. Some are developed from a priori considerations and are too detached from actual classificatory practice. Other theories of natural kinds are more naturalistic, but they posit overarching criteria for natural kinds that fail to capture the diversity of reasons scientists have for positing natural kinds. This paper highlights these problems and offers an account of natural kinds that better reflects actual classificatory practice in science. The account offered has two normative components. First, natural kind classifications should achieve the functions they are posited to attain, whether those functions are epistemic or non-epistemic. Second, how natural kind classifications achieve those functions should be grounded in the world and not merely in our thoughts about the world. The resultant account of natural kinds, the Grounded Functionality Account, is properly attuned to scientific practice and at the same time has a significant normative component
