Molecular characterization of measles viruses is an important component of measles surveillance because these studies enhance our ability to identify the source and transmission pathways of the virus. Molecular surveillance is most beneficial when it is possible to observe the change in virus genotypes over time in a particular region. Such information can help to document the interruption of transmission of measles virus and thus provide an important method for assessing the effectiveness of vaccination programs. It is recommended that virus surveillance be conducted during all phases of measles control and be expanded to give an accurate description of the global distribution of measles genotypes. This review provides updated information on the circulation patterns of measles genotypes and examples of the utility of virologic surveillance.