This chapter brings together and examines the various of naturalism in Kuhn’s thought throughout his career. Naturalism in philosophy of science can roughly be defined as the idea that in terms of method, philosophy and science are essentially engaged in the same enterprise, and thus the methods of the latter comprise the methods of the former. We begin by looking Kuhn remarks on the cognitive penetration in Structure and his brief post-Structure attempt to use the idea of stimuli to account for the latter. We then move onto a key plank of Kuhn’s philosophy, that of the role that similarity and dissimilarity relations play in concept acquisition and kind sortation. Finally, we examine Kuhn’s investigations into infant cognition in the written-up portion of Plurality of Worlds and how this played into his later taxonomic conception of science.