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About 40 000 Americans and 2 million people worldwide are newly infected with HIV each year. The combination antiretroviral regimen, tenofovir disoproxil fumarate (TDF)/emtricitabine, taken as a single pill once daily, has been shown to prevent HIV transmission but is used by fewer than 20% of people who could benefit in the United States.PubMed was searched on February 15, 2018, using the search terms pre-exposure, prophylaxis, HIV, and PrEP to identify English-language articles published between 2010 and 2018. Four placebo-controlled randomized clinical trials have demonstrated that preexposure prophylaxis (PrEP) with daily dosing of TDF/emtricitabine significantly reduces HIV acquisition in men who have sex with men, high-risk heterosexuals, and injection drug users who share injection equipment. The efficacy of daily TDF/emtricitabine exceeds 90% but is highly correlated with degree of adherence. TDF/emtricitabine is safe and well-tolerated. Only 2% of people discontinue PrEP because of adverse effects. Sexually transmitted infections are common among those using PrEP. Resistance to TDF/emtricitabine when used for PrEP is rare (<0.1%) and usually occurs when PrEP is inadvertently prescribed to individuals with undiagnosed acute HIV infection who have false-negative findings on HIV antibody/antigen testing due to HIV infection acquired within 7 to 10 days of testing. Effective methods are needed to identify individuals at high risk for acquiring HIV, ensure their access to PrEP, and maximize medication adherence.TDF/emtricitabine is an effective and safe therapy for preventing HIV transmission. Increasing prescription of TDF/emtricitabine for patients at risk of acquiring HIV has the potential to reduce new HIV infections.