The paper on Child and Adolescent Mental Health and Psychosocial Wellbeing Across the Life Course aims to inform research on child and adolescent mental health. It incorporates children’s developmental stages and the dynamic environment in which they live and grow. Informed by a review of existing theoretical frameworks on mental health and child development, it presents a framework that integrates elements of the socio-ecological model; the life course approach; the social determinants of health approach; and Innocenti Report Card’s Worlds of Influence Framework. Overall, this framework can be applied to support research and efforts to generate evidence, as well as to test and improve measures and methods for child and adolescent mental health.