The National Longitudinal Study of Adolescent Health (Add Health) is a longitudinal study of a nationally representative sample of more than 20,000 adolescents in grades 7-12 in the United States in 1994-95 who have been followed through adolescence and the transition to adulthood with three in-home interviews. In this application for a continuation of the Add Health Program Project, we propose to conduct a fourth follow-up interview with the Add Health cohort in 2007-08 when survey respondents will be aged 24-32, and propose a set of analysis subprojects that represents an interdisciplinary research program entitled "Add Health Wave IV: Social, Behavioral, and Biological Linkages." The scientific purpose of our Research Program is to study developmental and health trajectories across the life course of adolescence into young adulthood using an integrative approach that combines social, behavioral, and biomedical sciences in its research objectives, design, data collection, and analysis. In Wave IV we will collect longitudinal survey data on the social, economic, psychological, and health circumstances of our respondents, longitudinal geographic data, and new biological data to capture the prevailing health concerns of our Add Health cohort as well as biological markers of future chronic health conditions. We employ innovations in the collection of biological measures in a field setting on a large national sample that are both practical and ground-breaking. The combination of longitudinal social, behavioral, and environmental data with new biological data will expand the breadth of research questions that can be addressed in Add Health. Using an integrative life course theoretical framework, Program Project investigators have proposed significant new research on predisease pathways, gene-environment interactions, the relationship between personal ties and health, factors that contribute to resilience and wellness, the development of healthy relationships, and environmental sources of health disparities. With Wave IV, Add Health will provide the research community with a broad new set of opportunities to pursue interdisciplinary science, influence social and health policy, and improve the health and well-being of young people.