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" (1920, C.E.A. Winslow). It is concerned with threats to health based on population health analysis. The population in question can be as small as a handful of people or as large as all the inhabitants of several continents (for instance, in the case of a pandemic). The dimensions of health can encompass "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity", as defined by the United Nations' World Health Organization. Public health incorporates the interdisciplinary approaches of epidemiology, biostatistics and health services. Environmental health, community health, behavioral health, health economics, public policy and occupational health are other important subfields.

The focus of public health intervention is to improve health and quality of life through the prevention and treatment of disease and other physical and mental health conditions, through surveillance of cases and the promotion of healthy behaviors. Promotion of hand washing and breastfeeding, delivery of vaccinations, and distribution of condoms to control the spread of sexually transmitted diseases are examples of common public health measures.

Johns Hopkins (May 19, 1795 – December 24, 1873) was an American entrepreneur, abolitionist and philanthropist of 19th-century Baltimore, Maryland.

His bequests founded numerous institutions bearing his name, including Johns Hopkins Hospital, Johns Hopkins University, Johns Hopkins School of Nursing, Johns Hopkins School of Medicine, and Johns Hopkins Bloomberg School of Public Health.

A biography entitled Johns Hopkins: A Silhouette written by his cousin, Helen Hopkins Thom, was published in 1929 by the Johns Hopkins University Press.

Johns Hopkins was born on May 19, 1795, to Samuel Hopkins (1759–1814) of Anne Arundel County, Maryland, and Hannah Janney (1774–1864), of Loudoun County, Virginia. Home was Whitehall, a 500-acre (two km²) tobacco plantation in Anne Arundel County. His first name derives from a maternal great-grandmother, Margaret Johns, who passed it on to her son.

The Hopkins family were members of the Society of Friends (Quakers). In 1807 they emancipated their slaves in accordance with their local Society decree, which called for freeing the able-bodied and caring for the others, who would remain at the plantation and provide labor as they could. The second eldest of eleven children, 12 year-old Johns was required to work on the farm, interrupting his formal education. From 1806 to 1809, he likely attended The Free School of Anne Arundel County, which was located in today's Davidsonville, Maryland.