The UK has an unparalleled tradition of longitudinal birth cohort and panel studies that track generations of babies (and their families) from birth throughout the lifespan. The cohorts span over 70 years. The 1946 British Cohort Study and the 1958 National Child Development Study have been following the lives of over 20,000 people born in England, Scotland and Wales. These studies have been tracking study participants' height, weight, health, school performance, social class, deviance (e.g. bullying others, crime behaviours), and their later employment and relationship histories, health, life satisfaction and so on. Another study began in 1970; and then others in the 1990s and 2000s, including twin cohort studies, which can assess the relative importance of genetic and environmental influence on child development. Taken together, this research has made major contributions to UK health, education, economic and social policy, and to our understanding of individual development across the life course. The recent ESRC Longitudinal Studies Strategic Review noted that advances in longitudinal studies in other countries - including Japan - are now opening up key opportunities for rigorous international comparative studies on a wide range of issues including comparisons of life-course trajectories to better understand how environmental circumstances and policy can affect development trajectories, health and other outcomes. The Review also, however, noted that there is currently a lack of the right mix of skills and mentoring in quantitative 'know-how' to make these sorts of comparative analyses possible. More specifically, The Review highlighted the need for data harmonization to enhance international comparative research and improve its methodological foundations. This application aims to create sustainable international collaborations between UK and Japanese researchers to enable high-quality applications for future UKRI-JSPS bilateral research calls, as well as high quality peer-reviewed journal articles. We aim to bring together UK and Japanese researchers who are examining risk pathways to inform detection and prevention, fitting well with the ESRC's priority to understand social factors involved in mental health. To this end, we will utilise the pump-priming funds to (i) have a UK team deliver two workshops in Japan on data harmonisation and the estimation of developmental trajectories. We envisage that these workshops will act as a forum to begin a dialogue about wider harmonisation possibilities within existing cohort studies. (ii) The Japanese researchers will come to the UK to showcase existing projects and papers that arise from these workshops.