The RADx Data Hub Global Codebook defines a harmonized set of Common Data Elements (CDEs) to support retrospective harmonization of public health research data contributed to the NIH RADx Data Hub. The Codebook ensures semantic consistency across studies and enables cross-study integration, analysis, and reuse in alignment with the FAIR data principles. This Excel file includes the following sheets: 1_READ_ME: Introductory notes describing the purpose, structure, and usage of the codebook. 2_RADx_Global_Codebook: The full list of harmonized CDEs, including standard variable names, prompts, and enumerated response options. 3_RADx_UP, 4_RADx_rad, 5_RADx_TECH, 6_Digital Health: Program-specific mappings from original study variables to the Global Codebook CDEs for each RADx program (RADx-UP, RADx-rad, RADx Tech, and RADx DHT). 7_Identity_CDE1 through 24_Health_Stat_Cat_CDE12.4: Individual sheets documenting detailed harmonization for each CDE domain, such as race, ethnicity, age, sex, education, domicile, insurance status, employment, disability, medical history, symptoms, and health status (including general health, height, weight, and categorical health measures). Each domain sheet includes the original prompts and response values submitted by participating studies, as well as their aligned global equivalents. This structure supports transparent and reproducible harmonization, facilitating high-quality secondary use of RADx data.