This month's issue examines ethical dilemmas posed by epidemics—past and newly emerging. The clinical cases ask: What if a physician who may have TB refuses to seek treatment? How do physicians balance their dual obligations to family and society if they are asked to stay and treat patients during an epidemic? Can use of experimental treatments be justified in times of epidemic? What guidelines will help physicians who must enforce quarantine? Moving outward from the patient-physician relationship, research into infectious disease quickly leads to questions about the ethics of conducting research in underdeveloped countries and to the dual-use dilemma—how to study pathogens and prepare for bioterrorism while preventing malevolent misuse of those pathogens. Acknowledging the impact of infectious diseases on human history, a testimony from the first European plague of the 13th century and a meditation on how the AIDS epidemic forced medicine to examine its professional conscience are featured.