People from different cultures vary in the ways they approach social conflicts, with Japanese being more motivated to maintain interpersonal harmony and avoid conflicts than Americans are. Such cultural differences have developmental consequences for reasoning about social conflict. In the study reported here, we interviewed random samples of Americans from the Midwest United States and Japanese from the larger Tokyo area about their reactions to stories of intergroup and interpersonal conflicts. Responses showed that wisdom (e.g., recognition of multiple perspectives, the limits of personal knowledge, and the importance of compromise) increased with increasing age among Americans, but older age was not associated with wiser responses among Japanese. Younger and middle-aged Japanese showed greater use of wise-reasoning strategies than younger and middle-aged Americans did. This cultural difference was weaker for older participants’ reactions to interpersonal conflicts and was actually reversed for intergroup conflicts. This research has important implications for the study of aging, cultural psychology, and wisdom.