Measles virus (MV), a member of the Morbillivirus genus in the Paramyxoviridae family, is an enveloped virus with a nonsegmented negative-strand RNA genome and infects humans and nonhuman primates (Griffin, 2001). Despite the availability of vaccines, MV remains a major cause of childhood mortality, claiming roughly one million lives a year worldwide. The transient immunosuppression that accompanies and follows measles renders the patients susceptible to secondary infections accounting for most of measles-related complications and deaths. MV also causes postinfectious encephalitis, and in rare instances, subacute sclerosing panencephalitis, a persistent infection in the central nervous system. This review is concerned with the identification of a new MV receptor and its implication for understanding the pathology and pathogenesis of MV infection. MV was first isolated in primary human kidney cells inoculated with the blood and throat washings of a child with measles (Enders and Peebles, 1954). This first isolate, the Edmonston strain, was subsequently adapted to chicken embryo fibroblasts and became the progenitor for currently used attenuated vaccines. The Edmonston strain also grows well in continuous cell lines and has become the most extensively studied MV strain in laboratories. Vero cells, an African green monkey kidney cell line, had been commonly used for MV isolation until a decade ago, but several blind passages were usually required before virus propagation and development of cytopathic effect (CPE). Kobune et al. (1990) reported that an Epstein–Barr virus (EBV)-transformed marmoset B cell line B95-8 and its adherent subline B95a were highly sensitive to MV. Furthermore, they showed that MV strains isolated in B95a cells, but not Vero cell-isolated