Le LKD, Esturas AC, Mihalopoulos C, et al. - This study was intended to update 2 existing reviews of cost-effectiveness studies in this field in order to ascertain if such interventions are cost-effective. Researchers carried out searches of electronic databases (including MEDLINE, PsycINFO, CINAHL, and EconLit through EBSCO and Embase) for published cost-effectiveness studies of prevention of mental disorders and promotion of mental health and well-being from 2008 to 2020. A total of 65 studies were included, of which, 23 targeted children and adolescents, 35 targeted adults, while the remaining targeted older adults. The results showed that interventions for mental health prevention and promotion were cost-effective or cost-saving. The study observed that targeted prevention was likely to be cost-effective in comparison with universal prevention. The varied quality, as well as methodologies used in economic evaluations, limit the generalisability of conclusions about cost-effectiveness, although several interventions for mental health prevention and promotion provide good value for money.