 The EU Lifecycle Project is a large-scale research initiative that combines data from multiple cohorts across Europe and Australia. This project provides a comprehensive overview of mental health measures available in these cohorts, ranging from birth to adulthood. It also includes longitudinal and cross-sectional data on a variety of behavioral and psychopathology indicators and outcomes, such as executive function, depression, ADHD, and cognition. Additionally, the project has developed harmonized variables on a subset of mental health domains, which will allow for longitudinal meta-analysis across instruments and cohorts. This article was authored by Johanna L. Nader, Monica Lopez Vicente, Jordi Jilves, and others.