This article reports a cross-national study of developmental change in health-enhancing behavior--healthy eating and regular exercise--among adolescents in China and the United States. The application of a conceptual framework comprising psychosocial and behavioral protective and risk factors--both proximal and distal and at both the individual and social contextual level--is shown to provide a substantial account of variation in change in those behaviors over a 2-year interval. The explanatory account has generality across gender, the 3 grade cohorts, and most importantly, across the 2 markedly diverse societies.