Transgender women (assigned 'male'at birth with a female identity) are an understudied group with HIV prevalence rates in the range of 22 - 66%. Public health intervention research has produced no theory-driven, evidence-based interventions for transgender women. The unique cultural context of transgender women creates distinct risk factors that require systematic investigation and then integration into culturally relevant, community-based approaches to intervention. This K08 application describes a comprehensive, integrated training and research plan designed to serve as a pathway to scientific independence and the expertise to develop and test an innovative and urgently needed intervention to improve health outcomes among a highly marginalized population disproportionately affected by the HIV epidemic. The following training objectives are proposed: (1) to acquire expertise in the evaluation and application of theories of behavior change to marginalized populations;(2) to enhance skills in the use of mixed methods data collection and analysis, with an emphasis on techniques relevant to measurement development and theory testing;(3) to gain knowledge and experience with clinical trails methodology, including issues of sampling, randomization, design, protocol development, and ethics;and (4) to obtain training and experience in methods for developing, implementing, and evaluating culturally grounded, theory-driven HIV prevention interventions for transgender women. The specific research aims of the mentored original research are: (1) to describe the role of transgender women's unique cultural context on their HIV-related risk and protective factors;(2) to create new and to adapt existing quantitative measures to more accurately assess psychological dimension sand behavior relevant to transgender women's HIV risk and protective factors;(3) to identify psychosocial factors associated with HIV-related sexual and injection risk behaviors and protective factors among transgender women;and (4) to develop and test the feasibility and acceptability of a theory-driven, culturally grounded HIV prevention intervention for transgender women.