Pre-exposure prophylaxis, or PrEP, has been added to existing strategies to prevent HIV infection. PrEP requires a person who is HIV-negative to take a pill daily to reduce their risk of HIV infection. Studies have shown that PrEP reduces risk of infection in men who have sex with men as well as in heterosexual men and women.
Daily PrEP, with regular condom use and other HIV prevention methods, reduces HIV infection risk by up to 90%.
In July 2012, the U.S. Food and Drug Administration approved the combination of FTC-TDF, or Truvada®, for use as PrEP among sexually active adults at risk for HIV infection.
This video from whatisprep.org does a great job explaining what PrEP is and how it works: