PurposeThis study aimed to examine patterns of well-being across developmental stages and patterns of inequality in well-being among young adults and adolescents. Well-being exists when adolescents and young adults thrive and can achieve their full potential. MethodsWe used individual-level survey data from the Gallup World Poll from 164 countries between 2009 and 2017 (N = 446,934). Regression analyses were used to determine associations. ResultsWe documented substantial inequality in well-being across three developmental stages (adolescence, early adulthood, young adulthood). Health, education, income, and social relations are strongly associated with mean well-being and well-being inequality. We showed, for mean well-being, the relative importance of these factors varies over life-cycle stages. For inequality, most factors were consistent across developmental groups; however, we identified certain characteristics that were only relevant at certain developmental stages. DiscussionGiven the policy importance of well-being at all stages of life and the significance of adolescence and early adulthood in developing positive health-related behaviors, policies and programs targeting the highlighted characteristics are likely to be effective but require a multisectoral approach.