The National Longitudinal Survey of Public Health Systems (NALSYS) is a research initiative that tracks over 500 U.S. communities to study the implementation and impact of multi-sector population health activities. It collects data from local public health departments on various health improvement activities and the organizations involved, providing insights into the structure and evolution of public health delivery systems. By linking NALSYS data with other sources, researchers can analyze the effects of public health networks on outcomes like preventable mortality, hospitalizations, medical spending, and health equity.