This presentation details the historical and contemporary developments of the horizontal and vertical geodetic datums of the United States including: the North American Datum, North American Datum of 1927 (NAD 27), North American Datum of 1983 (NAD 83), the National Geodetic Vertical Datum of 1929 (NGVD 29) and the North American Vertical Datum of 1988 (NAVD 88), as well as the accepted global system, the International Terrestrial Reference Frame (ITRF). The session will highlight significant changes in measurement and positioning technologies and their impact on the development of reference ellipsoids, geoid models, and contemporary high accuracy reference frame enhancements. The presentation is designed to provide a foundation for further discussions that will focus on the rationale for national reference system changes by the National Geodetic Survey now scheduled for 2025.