Young Lives (YL) is the largest and most comprehensive mixed-methods longitudinal study in the Global South following the lives of 12,000 young people dispersed across more than 80 rural and urban sites in Ethiopia, India, Peru and Vietnam for the past two decades. The study offers a timely opportunity to examine risk and protective factors for mental health from infancy to young adulthood, something which is unique in a comparable multi- country setting. Identical assessments and measures in several domains (physical and mental health, cognitive, social-emotional) have been implemented over a 20-year period. This proposal will enhance the design and data collection of the seventh YL survey round to capture the mental health and subjective well-being of the 22- and 29-years old YL respondents; to include a cortisol measurement from individual hair samples to be used as an "objective measure" of stress and to collect information about young people’s experiences and responses to shocks, including climate-, covid-19- and conflict in the case of Ethiopia. We have the opportunity to contribute to the creation of unique open-access data providing an invaluable resource for our understanding of the lifetime and proximate risk and protective factors for young people’s mental health and well-being.