The International Society for Disease Surveillance (ISDS), in consultation with the CDC and the Council of State and Territorial Epidemiologists (CSTE), conducted a project to develop consensus-driven syndrome definitions based on ICD-10-CM codes. The goal was to have the newly created ICD-9-CM-to-ICD-10-CM mappings and corresponding syndromic definitions fully reviewed and vetted by the syndromic surveillance community, which relies on these codes for routine surveillance as well as for research purposes. The resulting tool, the Master Mapping Reference Table, may be leveraged by other federal, state, and local public health entities to better prepare and improve their surveillance, analytics, and reporting activities impacted by the ICD-10-CM transition.