Since 1999, the Agency for Healthcare Research and Quality has funded seven centers across the country to provide practical guidance to physicians and other health care professionals about the drugs they prescribe. These Centers for Education and Research on Therapeutics (CERTs) develop, translate and disseminate objective information on drugs to improve practice. The University of Pennsylvania’s CERTs focuses on developing evidence for optimal treatment strategies for infectious diseases, and promoting the judicious use of antibiotics to combat the problem of antibiotic resistance. This Issue Brief explores one of the fundamental challenges physicians face in optimizing antibiotic use: the potential conflict between what is best for an individual patient, and what is best for society as a whole.