Public health is the study and practice of managing threats to the health of a community. The field pays special attention to the social context of disease and health, and focuses on improving health through society-wide measures like vaccinations, the fluoridation of drinking water, or through policies like seatbelt and non-smoking laws.

The goal of public health is to improve lives through the prevention or treatment of disease. The United Nations' World Health Organization defines health as "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity." In 1920, C.E.A. Winslow defined public health as "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."

The public-health approach can be applied to a population of just a handful of people or to the whole human population. Public health is typically divided into epidemiology, biostatistics and health services. Environmental, social, behavioral, and occupational health are also important subfields.