Vaccination is the administration of antigenic material (the Vaccine) to produce immunity to a disease. Vaccines can prevent or ameliorate the effects of infection by a pathogen. It is considered to be the most effective and cost-effective method of preventing infectious diseases. The material administrated can either be live, but weakened forms of pathogens such as bacteria or viruses, killed or inactivated forms of these pathogens, or purified material such as proteins. Smallpox was the first disease people tried to prevent by purposely inoculating themselves with other types of infections; smallpox inoculation was started in India or China before 200 BC. In 1718, Lady Mary Wortley Montague reported that the Turks have a habit of deliberately inoculating themselves with fluid taken from mild cases of smallpox and she inoculated her own children. Before Edward Jenner tested the possibility of using the cowpox vaccine as an immunisation for smallpox in humans in 1796 for the first time, at least six people had done the same several years earlier: a person whose identity is unknown, England, (about 1771), Mrs. Sevel, Germany (about 1772), Mr. Jensen, Germany (about 1770), Benjamin Jesty, England, in 1774, Mrs. Rendall, England (about 1782) and Peter Plett, Germany, in 1791. In 1796 Edward Jenner inoculated using cowpox (a mild relative of the deadly smallpox virus). Pasteur and others built on this.

The term vaccination was first used by Edward Jenner an English physician 22 years later, in 1796. Louis Pasteur further adapted in his pioneering work in microbiology. Vaccination (Latin: vacca—cow) is so named because the first vaccine was derived from a virus affecting cows—the relatively benign cowpox virus—which provides a degree of immunity to smallpox, a contagious and deadly disease. In common speech, 'vaccination' and 'immunization' generally have the same colloquial meaning. This distinguishes it from inoculation which uses unweakened live pathogens, although in common usage either is used to refer to an immunization. The word "vaccination" was originally used specifically to describe the injection of smallpox vaccine.

Vaccination efforts have been met with some controversy since their inception, on ethical, political, medical safety, religious, and other grounds. Early success and compulsion brought widespread acceptance and mass vaccination campaigns were undertaken which are credited with greatly reducing the incidence of many diseases in numerous geographic regions. The eradication of smallpox, which was last seen in a natural case in 1977, is considered the most evident success of vaccination.