Public health has become a broad and flexible concept that encompasses both the traditional definition of practices that benefit the health of the community and personal health services, such as hypertension treatment. Legally, however, the basis for traditional public health and personal health services are very different. For example, although the state has broad powers to order vaccination to prevent the spread of a dangerous communicable disease, the state has limited power to require competent adults to undergo medical treatment for personal illness such as hypertension.

The core of public health law is coercive action under state authority, the police power. In the best of circumstances, this authority may be needed only to encourage educational efforts. At other times, however, public health authorities must seize property, close businesses, destroy animals, or involuntarily treat or even lock away individuals. Such powers are rooted in earlier times, when the fear of pestilential disease was both powerful and well founded. As communicable diseases such as smallpox, tuberculosis, and polio were brought under control in the 1960s, the public and even some public health experts began to believe that there was no longer a need for coercive public health measures.

The terrorist attack on the United States on September 11, 2001, followed shortly by anthrax-laden letters sent to public figures, brought bioterrorism to the public's consciousness, reviving ancient fears of pestilence. The sequella of Hurricane Katrina and growing fears of pandemic flu have raised questions about the capabilities of the public health infrastructure and the potential reach of public health laws in an emergency. These fears have forced a rethinking of public health law authority.