For adults, ownership is nonobvious: (a) determining ownership depends more on an object's history than on perceptual cues, and (b) ownership confers special value on an object ("endowment effect"). This study examined these concepts in preschoolers (2.0-4.4) and adults (n = 112). Participants saw toy sets in which 1 toy was designated as the participant's and 1 as the researcher's. Toys were then scrambled and participants were asked to identify their toy and the researcher's toy. By 3 years of age, participants used object history to determine ownership and identified even undesirable toys as their own. Furthermore, participants at all ages showed an endowment effect (greater liking of items designated as their own). Thus, even 2-year-olds appreciate the nonobvious basis of ownership. (Contains 5 figures and 1 table.)