PROJECT SUMMARY/ABSTRACT The five-year training and research project outlined in this application will foster the career of Dr. Abigail Greenleaf, an already accomplished scholar in cross-sectional data collection and analysis to master high-frequency, longitudinal health analyses to impact health outcomes. With the proposed career development and research activities, the candidate will be poised to make significant contributions in the field of global reproductive population studies meant to better understand family building desires and patterns of transition to adulthood. This Mentored Research Scientist Development award is designed to meet Dr. Greenleaf’s near-term career development goal of understanding contraceptive dynamics – adoption, continuation, discontinuation, and switching – among adolescent girls and young women and to meet her overarching career goal to become an independent scholar who advances knowledge of reproductive health and family formation. Thus, the K01 research will be supported by mentor-guided career development training in four complementary areas to facilitate her long-term research goals. To enrich her reproductive health scholarship, Dr. Greenleaf will be (1) train in sociological theories of pregnancy desire; (2) learn to analyze high-frequency longitudinal data; and (3) gain expertise in prevention and risk of HIV acquisition. Finally, to become an independent NIH-funded investigator, Dr. Greenleaf will (4) undertake professional development activities. This innovative proposal aligns with NICHD’s 4th key research priority: Improving Child and Adolescent Health and the Transition to Adulthood. The research plan has three aims: (1) Investigate how changing states (schooling, income, residential mobility) impact contraceptive use; (2) Examine the relationship between pregnancy desires and contraceptive use; (3) Test whether changes in a woman’s perception of her HIV risk changes her probability of contraceptive use and HIV prevention behaviors. Career development and research activities will be supervised by a team of mentors including primary mentor Dr. Elaine Abrams, Professor of Epidemiology and Pediatrics at Columbia University and two co-mentors: Dr. Jennifer Barber, Sociology Professor, Indiana University; and Dr. John Santelli, Professor, Heilbrunn Department of Population and Family Health and Pediatrics at Columbia University. The proposed K01 project will place Dr. Greenleaf in a unique and important position to conduct truly innovative studies of contraceptive and HIV-prevention behavior among adolescent girls and young women worldwide, a priority population for reaching global reproductive health improvements.