We examined English and Spanish speakers' reliance on defining and characteristic features in developing definitions of objects and events. Native monolingual English- and Spanish-speaking kindergartners, second graders, fourth graders, and adults participated in a task in which they were presented with brief stories, and judged whether or not the story described particular terms. We found that both English and Spanish speakers increasingly relied on defining features with development, and that they relied on characteristic features to a smaller but constant degree throughout development. We also found that Spanish speakers were more likely to rely on defining as opposed to characteristic features for the objects, whereas English speakers were more likely to rely on defining features for the events, especially at certain points in development. We discuss the implications for theories of semantic and conceptual development.