Statutes and regulations are frequently designed to affect the public in specific ways. But exactly how these laws ultimately impact the public often depends on how politicians go about securing control of the complex public agencies that implement policies, and how these organizations in turn are used to define the often-contested concept of "national security." Governing Security explores this dynamic by investigating the surprising history of two major federal agencies that touch the lives of Americans every day: the Roosevelt-era Federal Security Agency––which eventually became today's Department of Health and Human Services––and the more recently created Department of Homeland Security. By describing the legal, political, and institutional history of both organizations, Mariano-Florentino Cuéllar offers a compelling account of crucial developments affecting the basic architecture of our nation. He shows how Americans end up choosing security goals not through an elaborate technical process, but in lively and overlapping settings involving conflict over statutory programs, agency autonomy, presidential power, and priorities for domestic and international risk regulation. Ultimately, as Cuéllar shows, ongoing fights about the scope of national security reshape the very structure of government and the intricate process through which statutes and regulations are implemented, particularly during––or in anticipation of––a national crisis.