A vertical datum or height datum is a reference surface for vertical positions, such as the elevations of Earth features including terrain, bathymetry, water level, and man-made structures; in any particular case one must be assigned even if arbitrarily, and commonly adopted criteria for a vertical datum include the following approaches:

Prominent vertical datum in use by professionals include the National Geodetic Vertical Datum of 1929 and the North American Vertical Datum of 1988.