Tatiana Salisbury (Centre for Global Mental Health, King’s College London) and Kelly Rose-Clarke (Department of Global Health and Social Medicine, King’s College London) discuss why it’s important to invest in child and adolescent mental health, and outline key messages for donors and how they can deliver for mental health. This video was produced in Summer 2019, for DFID staff, as part of the K4D Learning Journey “Leave No One Behind”: Delivering on the 2030 Sustainable Development Agenda for Mental Health and Psychosocial Disabilities.