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.By itself measles virus infection has and still provides some of the most interesting phenomena in biology. Following infection of dendritic cells, measles virus causes a profound suppression of the host 's immune response that lasts a number of months after apparent recovery from infection. Indeed, measles virus was the first virus to be associated with immunosuppression with many of the manifestations to be observed one hundred years later with HIV infection. Measles is also associated with development of both post-infectious encephalomyelitis, an autoimmune demyelinating disease, and subacute sclerosing panencephalitis, a slowly progressive neurodegenerative disorder. How measles virus infects cells, spreads to various tissues and causes disease, as well as the role of the immune response, generation of new vaccines, and use as a vector for gene delivery are topics covered in these two volumes.