Research in cognitive development has highlighted important differences between conceptions of natural kinds and artifacts. One interpretation of the distinction is that natural kinds are categories one discovers, whereas artifactual kinds are invented. Four studies assessed whether children and adults saw categorization decisions as objective matters of fact or as invented conventions. Preschool-age children treated basic-level categories of animals and human-made artifacts as objective. At the superordinate level, kinds of animals were treated as more objective than were kinds of artifacts. In general, adults' judgments were similar to children's. Both children and adults have reliable and differentiated intuitions regarding category objectivity. The results from these studies are discussed in terms of their implications for structural and theory-based accounts of category naturalness.