Throughout history, emerging and reemerging infectious disease have plagued human populations. From the earliest recorded epidemics of bubonic plague and smallpox more than 2,500 years ago to the deadly 1918 pandemic of the Spanish Flu, infectious diseases have helped to shape human history. Despite significant advances in medical research and treatment in the past century, infectious diseases remain among the leading causes of death worldwide. These diseases are appearing in places they have never been seen before or were thought to have been eradicated, are spreading faster and more frequently, and are posing an increasing global health threat that will affect national and international security in both the near- and long-term future, even affecting the success of U.S. military missions and operations.