As part of the OECD project The Contribution of Migration to Regional Development (OECD, 2022), the OECD has engaged in an extensive data collection effort. The Municipal Migration database offers unprecedentedly detailed information on the subnational geography of migration in OECD countries. Based on data from continuous population registers as well as censuses, the database contains population statistics for 22 OECD member countries between 1991 and 2022, primarily at the level of municipalities. The databased was compiled using publicly available data (mainly from National Statistical Offices) and data harmonisation ensures consistency of the data over time despite changes to municipal boundaries.