Over the last decade, a number of concerns have arisen related to safety issues that have had an adverse effect on the public's trust, particularly among parents whose children are the primary recipient of the vaccine. Historically, the live attenuated measles virus (MV) vaccine and the combination multivalent measles, mumps, and rubella (MMR) vaccine have had a major impact on the health of children worldwide and have been extremely successful at preventing infectious diseases associated with three childhood viral pathogens. In this report, we describe MV infection, replication, pathogenesis, and immunization. MV is a viral pathogen that exhibits a number of complex processes that can effect its replication, pathogenesis, and the induction of an effective antiviral immune response. We describe the published literature as it relates to MV infection and immunization and report adverse events in an attempt to provide a balanced discussion and an historical perspective of the MMR vaccine and autism.