Measles virus, one of the most contagious of all human viruses, has been largely contained by the development and use of a vaccine that was introduced 50 years ago. These two volumes were timed to honor the introduction of the vaccine and to record the enormous advancements made in understanding the molecular and cell biology, pathogenesis, and control of this infectious disease. Where vaccine has been effectively delivered, endemic measles virus transmission has been eliminated. However, difficulties in vaccine delivery, lack of health care support and objection to vaccination in some communities continue to result in nearly 40 million cases and over 300,000 deaths per year from measles.