What are pandemics? The National Institutes of Health proposed pandemics must meet eight criteria: wide geographic extension, disease movement, high attack rates and explosiveness, minimal population immunity, novelty, infectiousness, contagiousness, and severity. The introduction explains that much of the way we confront pandemics now has been shaped by the past history of pandemic and epidemic disease. There is a clear relationship between disease and social conditions, conditions that do not exist everywhere and that will not be alleviated with biomedicine. The question of susceptibility—who gets a disease and why—is also important. Epidemics and pandemics cannot occur without a dense and mobile population.