Preexposure prophylaxis (PrEP), in which HIV-uninfected persons with ongoing HIV risk use antiretroviral medications to reduce their risk of acquiring HIV infection, is an efficacious and promising new HIV prevention strategy. The past 2 years have seen significant new advances in knowledge regarding PrEP, including definitive demonstration that PrEP reduces the risk of HIV acquisition, regulatory approval of combination oral emtricitabine/tenofovir disoproxil fumarate (FTC/TDF) as the first PrEP agent with a label indication for sexual HIV prevention, and the development of normative guidance for clinical prescribing of PrEP. In PrEP clinical trials, HIV protection was strongly correlated with PrEP adherence; therefore, understanding and supporting adherence to PrEP are key to maximizing its public health impact. As would be expected for any new HIV prevention approach, questions remain, including how to motivate uptake of and sustain adherence to PrEP for HIV prevention in high-risk populations, how much use is sufficient to achieve HIV protection, and the potential of “next-generation” PrEP agents to improve this effective prevention strategy. At this important transition point—from demonstration of efficacy in clinical trials to thinking about implementation and effectiveness—this review addresses where we have been and where we are going with PrEP for HIV prevention.