Measles is an infectious disease that is caused by a virus and primarily infects children. The symptoms of measles include high fever, headache, hacking cough, conjunctivitis and a rash which usually begins inside the mouth as white spots, (called Koplik's spots) and progresses to a red rash that spreads to face, neck, trunk and extremities. The incubation period varies but is usually 10-12 days until symptoms appear. Measles are sometimes called rubeola or the nine-day measles. Normally recovery is full. However, complications can arise if a secondary bacterial infection occurs, such as pneumonia or ear infection.

Measles was described as long ago as the ninth century when a Persian physician, Rhazes, first differentiated between measles and smallpox. He also made the observation that fever is a defense the body has against a disease, not a disease itself. His writings on the subject were translated into English and published in 1847.

The measles virus was first discovered in the 1930s; John F. Enders of Children's Hospital in Boston eventually isolated the measles virus in 1954 and began looking for an attenuated strain to be suitable for a live-virus vaccine. A successful immunization program for measles was begun soon after. Today measles is controlled in the United States with a vaccination that confers immunity against measles, mumps and rubella and is commonly called the MMR vaccine. Since a series of measles epidemics occurred in the teenage population, a second MMR shot is now required of many school-age children as it was found that only one vaccination appeared not to confer lifelong immunity.