To provide health policy researchers with access to Medicaid administrative data in a form that is suitable for research, the Centers for Medicare & Medicaid Services (CMS) has funded and overseen the development of an annual Medicaid Analytic Extract (MAX). MAX includes enrollment and claims information for each person enrolled in Medicaid and a subset of those enrolled in the Children’s Health Insurance Program (CHIP) through a separate child health program (S-CHIP). While the MAX data have supported extensive research on state Medicaid programs and enabled detailed cross-state comparisons, their application to national-level and longitudinal research has been limited by the fact that the files do not identify records belonging to the same individual over time or across states.