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Public health is defined as “the efforts organized by society to protect, promote, and restore the people’s health…directed to the maintenance and improvement of the health of all the people through collective or social actions.”1 The public health system is a complex network of organizations working together collectively to assure conditions in which society can be healthy.2,3 This system includes a wide array of government agencies, private organizations, public health departments, community health centers, healthcare systems, advocacy groups, the media, and social service agencies. The governmental role to protect the public’s health is represented by public health agencies at several levels of responsibility: federal, tribal, state, territorial, and local.4

Public health contributes tremendous value to society. Its prevention efforts are responsible for 25 years of the nearly 30-year improvement in life expectancy at birth in the United States over the past century. This is based on evidence that only about 5 years of the 30-year improvement are the result of medical care.5 Public health approaches carry significant potential for future contributions as well, since almost half of all deaths in the United States are premature and result from preventable causes.6 This chapter will review the structure and function of public health in the United States. (Also see Chap. 9: Public Health Practice in the United States.)


Public health is practiced in a variety of settings by a variety of professionals. Although community-based organizations and health systems contribute to the practice of public health, it is typically associated with a constellation of activities at the federal, state, and particularly, local levels. Unlike many community-based organizations, only official public health agencies have statutory responsibility for the health status of the populations they serve. Legal authority for this responsibility is based on a variety of federal, state, and local ordinances, including the granting of police powers.

The structure and function of modern public health in the United States has accelerated dramatically following a 1988 IOM report that described the public health system as being in disarray, with no coherent vision or mission.2 Adding to this impetus were the threats of terrorism and the expanding role of public health in addressing social determinants of health in an era of increasing social disparity. Previous approaches to illness and health have been replaced with a new understanding of the complex relationship between social issues, cultural factors, genetics, behavior, illness care, and prevention. Today, public health spans almost all health discipline, relying upon the three core functions of public health: Assessment, Policy Development, and Assurance.

Public Health’s Three Core Functions

It has been over 30 years since the IOM identified the three core functions for governmental public health departments: Assessment, Policy Development, and Assurance.2 These core functions are described below.


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