Summary This proposal seeks continued funding to expand and enhance the IPUMS Health Surveys Project. IPUMS Health Surveys provides streamlined access to core U.S. survey data on population health through two integrated databases: the National Health Interview Survey (IPUMS NHIS) and the Medical Expenditure Panel Survey Household Component (IPUMS MEPS). The NHIS is the leading source of information on U.S. health, health disparities, the social determinants of health, and health systems change; the MEPS is the primary source of information on national trends and correlates in health care spending. The proposed project will further improve this crucial resource for pathbreaking research in five ways: (1) Harmonization of redesigned NHIS. NHIS has been significantly redesigned in 2019. Several aspects of the redesign represent major departures from past practice and have implications for the comparability of the data over time. This project will create and modify existing IPUMS NHIS data and metadata to accommodate these changes to the survey, including documenting changes to the data collection procedures and data structure so users can develop analyses that bridge the survey redesign period to the fullest extent possible. (2) Database expansion. This project will expand IPUMS Health Surveys by integrating five new years of NHIS and MEPS survey data and documentation. In each year, the surveys will add, drop, and modify questions. The proposed project will accommodate and document those changes without losing detail. (3) MEPS enhancements. This project will enhance the IPUMS MEPS database by incorporating data from the 1996-2023 medical conditions and event files, documenting relationships among condition files, event files, and rounds and describing the relationships between the different file types and the data already available through IPUMS MEPS in machine-readable metadata that will be used to create new user-facing tools. (4) Data infrastructure and access improvement. The proposed project will enrich access to the data with three new approaches: (a) design and implement a variable construction system on the IPUMS MEPS website; (b) support online data analysis of the IPUMS MEPS data through a new online data tabulator; and (c) develop an Application Programming Interface (API) to facilitate programmatic access to MEPS and NHIS data. (5) Dissemination. Through user support, training, and outreach activities, the proposed project will attract new users and support continuing use of the IPUMS NHIS and IPUMS MEPS data. Along with conference exhibits and presentations, introductory workshops, and timely answers to user queries, the project will provide new introductory webinars, in-depth webinars covering specific topics, and two multiple-day workshops to train early-career scholars to use IPUMS MEPS.