Governing Security investigates 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 Cuellar 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 Cuellar 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.