Across 3 experiments, we found evidence that information about who owns an artifact influenced 5- to 10-year-old children's and adults' judgments about that artifact's primary function. Children's and adults' use of ownership information was underpinned by their inference that owners are typically familiar with owned artifacts and are therefore likely to know their primary functions. Accordingly, when this inference was undermined--when an artifact's owner was said to be unfamiliar with the owned artifact--ownership was no longer used as a privileged heuristic cue to artifact function. These experiments also revealed age-related differences in how ownership information was prioritized relative to another well-studied source of information known to influence artifact cognition, namely, information about an artifact's original designer-intended function. Specifically, older children and adults were more likely than younger children to prioritize design information over ownership information. Our results suggest that children and adults differ in how they weight the relative importance of these 2 sources of function-relevant information--likely reflecting age-related changes in children's and adults' sensitivity to ownership and design information across development.