Mental illnesses represent a huge burden for society, the economy, and the aMental illnesses represent a huge burden for society, the economy, and the affected individuals. To significantly increase citizens? mental health, today?s symptom-based diagnoses need to be complemented by biological criteria accounting for individual and sex differences. Furthermore, early detection and prevention measures need to be improved. RE-MEND addresses the current gaps and challenges with an interdisciplinary approach by: i) focussing on four critical life stages in which an individual?s susceptibility to mental illness is strongly influenced by changes in endocrine signalling, including sex hormones, namely early life, puberty, peripartum, and transition into old age; ii) integrating data from large population-based longitudinal cohort studies allowing for discovery of risk and protective factors as well as biological patterns that influence mental states in the general population across these life stages; iii) complementing epidemiological with experimental studies to establish correlative and causative links leading to mechanistic understanding; iv) using advanced biostatistics as well as machine learning and artificial intelligence for data integration and biomarker and drug target discovery; v) combining the biological approaches with communication science studies to efficiently translate its results to societal impact. Ultemately, RE-MEND will result in: i) Significantly increased mental health literacy among stakeholders and citizens; ii) Validated biomarkers for assessing mental health state and its predisposition as well as more accurate diagnoses and personalised preventive and therapeutic measures; iii) Recommendations for early detection, better prevention, and drug design strategies to protect vulnerable individuals from mental illness in sensitive life stages; and iv) strategies on how these advances can be used to decrease stigma and increase prevention behaviour.