A look at PrEP, a prevention strategy for people at high risk for contracting HIV. Researchers at the University of California explain how pre-exposure prophylaxis (PrEP) works as they describe a four-year, multi-pronged study of men who have sex with men in Los Angeles and San Diego. Participants agree to take a Truvada pill daily to reduce their risk of getting infected by up to 99%. But will they follow through? Methods to increase adherence among the participants are also being tested, including daily reminders via text messages and tracking usage of the medication with special Mems caps for the pill bottles.