The Spanish Flu pandemic, the deadliest in history, infected some 500 million people worldwide and killed 20 to 50 million. In the hundred years since, medicine has made great strides—substituting flu shots for whiskey and blood-letting, for instance—but the disease still kills more than 30,000 each year in the U.S. In this comprehensive history of the notoriously infectious and adaptable virus, Brown, a veteran emergency room doctor now directing NIH’s Office of Emergency Care Research, draws on interviews with epidemiologists, policy makers, and the researcher who sequenced the genes of the 1918 pathogen to retrace past efforts to combat influenza and better prepare for future outbreaks.