PROJECT SUMMARY/ABSTRACT Expedited Partner Therapy (EPT) offers a unique tool to combine HIV prevention and STI control through an integrated HIV Prevention Cascade. In providing empiric, patient-delivered antibiotic treatment to the recent sexual partners of individuals with bacterial STIs, EPT promotes partner notification, HIV/STI testing, and treatment, and triggers the critical first step of an HIV prevention cascade culminating in uptake of antiretroviral-based prevention methods (such as PrEP or pre-exposure prophylaxis), and ultimately a reduction in community-level HIV transmission risk. By targeting the sexual partners of individuals with new STI diagnoses, EPT provides an opportunity to identify nodes of active HIV and STI transmission within high-risk sexual networks, to promote HIV testing and linkage to prevention and treatment services among these individuals, and to potentially reducing the incidence of HIV/STI transmission within the larger population. Use of EPT for HIV/STI control among MSM presents three key questions for future research: i) What is the impact of EPT on biological outcomes of persistent or recurrent bacterial STIs among MSM? ii) What is the effect of EPT on prevention cascade outcomes of partner HIV/STI testing and linkage to HIV prevention/treatment services? and iii) Would any observed increases in prevention cascade outcomes lead to community-level reductions in HIV/STI transmission? Aim 1 (Individual). To determine the effect of EPT on individual-level outcomes of partner notification and persistent or recurrent GC/CT infection among MSM. Aim 2 (Partnership). To assess the impact of EPT on partner-level outcomes of notification, testing, STI treatment, and linkage to HIV prevention and treatment services. Aim 3 (Population). To use Agent Based Modeling to estimate the impact of EPT for MSM on HIV/STI transmission at network- and population-levels.