The United States Public Health Service is a collection of agencies of the Department of Health and Human Services concerned with public health, containing nine out of the department's twelve operating divisions. The Assistant Secretary for Health oversees the PHS. The Public Health Service Commissioned Corps (PHSCC) is the federal uniformed service of the PHS, and is one of the eight uniformed services of the United States.

Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals". Analyzing the determinants of health of a population and the threats it faces is the basis for public health. The public can be as small as a handful of people or as large as a village or an entire city; in the case of a pandemic it may encompass several continents. The concept of health takes into account physical, psychological, and social well-being.