I will conduct four studies applying advanced quantitative methods and cross-sectional and longitudinal study designs using a current ESRC-funded UK birth cohort from an interdisciplinary perspective, aiming to address the major societal challenge of co-occurring antisocial behaviour (AB) and substance use (SU) in young people, answering unsolved questions about the mechanisms driving the co-occurrence of these conditions from mid-adolescence to early adulthood. Findings will help inform the prevention and intervention programmes for AB or SU alone or in combination, with potential benefits for young people and their families, mental health researchers, education and legal practitioners and services, and policymakers.