The burden of mental health conditions and poor psychosocial wellbeing among children and adolescents is associated with significant lifetime costs, as mental health conditions is associated with learning lower educational attainment and impeding the development of socioemotional skills which translates into reduced earning potential and labor productivity in later life. The humanitarian emergencies further exacerbate these impacts. A critical point, however, is that these costs to individuals, communities and countries can be mitigated through mental health and psychosocial support (MHPSS) interventions that aim to promote mental health and wellbeing and/or prevent and respond to mental health conditions, thereby promoting learning and educational outcomes. This global cost-benefit analysis (global CBA) firstly estimates the global economic costs of mental health conditions through the effect on school completion, and poor social and emotional wellbeing among children and adolescents aged 10-17 years affected by humanitarian emergencies. It then models the economic benefits of addressing the mental health needs of children and adolescents through mental health and psychosocial support interventions. [This report was written by Angie Jackson-Morris, Michael Onah, Christina L. Meyer, Lily Morrell, and Rachel Nugent.]