Linked birth and infant death certificates allow measurement of birthweight-specific infant mortality. Jack Smith, MS, to whom this issue of the American Journal of Preventive Medicine is dedicated, played a key role in the National Infant Mortality Surveillance (NIMS) project. NIMS provided national data on birthweight-specific infant mortality for the 1980 birth cohort, updated data previously collected by the National Center for Health Statistics (NCHS) for the 1960 birth cohort, and supported NCHS's implementation of an annual linked file in 1983. NIMS illustrated themes in infant mortality that remain important: the role of low birthweight (LBW) as a contributor to infant mortality, the contribution of disparities in LBW and birthweight-specific mortality to black-white gaps in infant mortality, and the nation's greater success in reducing mortality among LBW infants than in preventing LBW. Linked birth and infant death records are used nationally and by states to study an array of maternal and infant health topics, from the quality of vital records to the impact of therapeutic and public health interventions. By supplementing birth and infant death records with linkages to program and hospital discharge data, epidemiologists and health service researchers are extending the utility of vital statistics data to monitor maternal and infant health.