Project Summary/Abstract Pre-exposure prophylaxis (PrEP) can prevent HIV infection among persons who inject drugs (PWID). However, PrEP use among PWID is low and there have been several recent HIV outbreaks among PWID throughout the United States. Few studies have focused on PrEP for PWID although many PWID are eligible for PrEP. A significant barrier to PrEP for PWID is stigma (i.e., social devaluation and discrediting), especially stigma related to drug use, which can translate into negative healthcare interactions and/or healthcare avoidance as well as healthcare providers being less willing to prescribe PrEP to PWID. PWID may have multiple characteristics that could be stigmatized such as drug use, race/ethnicity, sexual identity, gender, and poverty, as well as stigma attributed to HIV and PrEP. In addition, PWID may experience stigma at the organizational level (e.g., in healthcare, drug treatment, pharmacies, or syringe exchange programs) or at the structural level in the form of state policies. It is important to understand how these multiple characteristics create unique stigma experiences (i.e., intersectional stigma – stigma characteristics that are experienced simultaneously) among sub-populations of PWID that could affect PrEP and service use. The purpose of this research is to understand intersectional stigma among PWID and how it affects PrEP and other service use though the following specific aims: (1) Identify sub-populations of PWID that display different patterns of stigma due to drug use, race/ethnicity, sexual identity, gender, and poverty; (2) examine associations of patterns of stigma with PrEP willingness and uptake and other service-related variables over time; (3) evaluate how and if covariates (sociodemographic variables, HIV and PrEP stigma, and structural stigma by state) moderate associations of stigma with PrEP use and other service use. The results of this study will inform PrEP implementation broadly, as well as inform the development of stigma and PrEP interventions tailored to sub- populations of PWID. The research project is part of a comprehensive training program designed to facilitate Dr. Walters transition to research independence. Training aims include (1) Building topical expertise in intersectional stigma experienced by PWID; (2) Develop methodological expertise in latent variable modeling and effect modification; (3) Gain training in intervention science; (4) Gain expertise in ethical conduct of research pertaining to HIV prevention among PWID; and (5) Strengthen professional skills for a successful independent research career.