Despite increasing usage of HIV PrEP among populations at substantial risk of infection in the U.S. there remains a gap between recommended and actual levels of use. This project aims to explore transmission dynamics among MSM by investigating the integration of event-driven PrEP regimens in the context of current daily oral PrEP use among MSM, and the implications of clinical practice guideline elements (medication risk profile and ancillary services engagement) in the context of racial/ethnic disparities and geographic differences.