The social norms that guide boys' transitions through puberty and young adulthood are factors associated with high risk of HIV in sub-Saharan Africa (SSA). Yet few methodologies exist that adequately capture these norms and interpret their influences for response and intervention. A deeper understanding of the gendered norms societies are conveying to boys as they transition through puberty, and how best to shift those norms contributing to risky behavior, is critical for protecting both young men and their future sexual partners from acquiring HIV. Although a growing body of research exists on masculinity and HIV risk, the majority of studies were not conducted in SSA, the region with the highest HIV risk for adolescents; and few to no studies engaged boys themselves as a source of recommendations for future intervention. The objective of this small research grant (R03) is to develop a research methodology for engaging adolescent boys in the process of identifying the gendered influences shaping their transitions through puberty, the ways in which such influences shape boys' and girls' vulnerabilities to HIV, and how such influences can most effectively be addressed through intervention from the perspective of boys themselves. We propose the following specific aims: 1) To develop a novel in-depth participatory and dynamic methodology for ascertaining adolescent boys' experiences of transitioning through puberty and the gendered norms that are most influential in shaping young men's beliefs and behaviors related to masculinity, male sexuality, gender-based violence, and HIV risk. 2) To field test the methodology with a sample of 50 boys aged 16-19 in Tanzania in and out of school 3) To ascertain from adolescent boys the most effective approaches for shifting local masculinity norms that put them (and their future sexual partners) at risk of HIV and other sexually-transmitted infections (STIs), and to utilize this exploratory data for the development of an R01 intervention and evaluation grant application. To accomplish these aims, we propose to conduct a two-year collaborative research study with adolescent and sexual-health researchers at Muhimbili University of Health and Allied Sciences (MUHAS) in Tanzania. The process of developing and testing the methodology in Tanzania will provide important preliminary findings in the Tanzania setting for the conceptualization of a boy's puberty book intervention, to be developed and evaluated through an R01 application (to be submitted at the completion of this R03 study), and will also serve as a model for other SSA countries interested in understanding and addressing the gendered norms impacting on adolescent risk of HIV and other STIs within their countries.