Individualism-collectivism is one of the best researched dimensions of culture in psychology. One frequently asked but underexamined question regards its cross-temporal changes: Are cultures becoming individualistic? One influential theory of cultural change, modernization theory, predicts the rise of individualism as a consequence of economic growth. Findings from past research are generally consistent with this theory, but there is also a body of evidence suggesting its limitations. To examine these issues, cross-temporal analyses of individualism-collectivism in the United States and Japan were conducted. Diverging patterns of cultural changes were found across indices: In both countries, some of the obtained indices showed rising individualism over the past several decades, supporting the modernization theory. However, other indices showed patterns that are best understood within the frameworks of a shifting focus of social relationships and a persisting cultural heritage. A comprehensive theory of cultural change requires considerations of these factors in addition to the modernization effect.