This　paper　traces　the　nearly　century-long　research　history　of　transmission　error　(TE)　of　gear,　highlighting　three　stages　of　understanding　TE　from　geometric　error,　kinematic　error,　and　dynamic　error.　The　relationship　between　TE　and　elemental　gear　deviations　is　discussed,　and　the　classification　of　TE　is　proposed.　Furthermore,　the　composition　of　TE　is　clarified,　emphasizing　their　dynamic　nature.　The　application　of　TE　in　various　areas,　such　as　gear　design,　process　error　analysis,　transmission　chain　accuracy　characterization,　and　gear　NVH　evaluation,　is　summarized.　Finally,　the　limitations　and　deficiencies　of　TE　are　outlined,　and　a　resolution　to　solve　these　problems　is　proposed　by　considering　gear　pair　integrated　errors.　©　FTM　2024.All　rights　reserved.