: According to the latest World Bank estimates, over the past decade some US $4.3 billion has been pledged by governments to combat the threat of pandemic influenza. Presidents, prime ministers, and even dictators the world over have been keen to demonstrate their commitment to tackling this disease, but this has not always been the case. Indeed, government-led intervention in responding to the threat of pandemic influenza is a relatively recent phenomenon. I explore how human understandings of influenza have altered over the past 500 years and how public policy responses have shifted accordingly. I trace the progress in human understanding of causation from meteorological conditions to the microscopic, and how this has prompted changes in public policy to mitigate the disease's impact. I also examine the latest trend of viewing pandemic influenza as a security threat and how this has changed contemporary governance structures and power dynamics. (Am J Public Health. Published online ahead of print November 17, 2011: e1-e9. doi:10.2105/AJPH.2011.300330).