Pre-exposure prophylaxis (PrEP) is a new potential HIV prevention strategy in which high-risk HIV-uninfected persons take antiretroviral medications prior to HIV exposure to reduce the risk of acquiring HIV. Large clinical trials of PrEP are ongoing worldwide, with results expected during the next few years. This session will review the scientific rationale behind PrEP, summarize the ongoing clinical trials, and look forward to possible PrEP implementation.