Among the most important medicines ever discovered, antimicrobial agents have saved millions of lives and improved the outcomes for countless patients since these drugs were introduced in the early 1930s. However, the effectiveness of these lifesaving resources is at risk. Many medical advances that physicians and patients take for granted—including cancer treatment, surgery, transplantation, and neonatal care—are endangered by increasing antibiotic resistance and a distressing decline in the antibiotic research and development pipeline.1