The outstanding performance of the global GOCE geoid enables new applications like unification of height systems worldwide, for which the global geoid needs to be known with high quality. This study aims at identifying the impact of the GOCE mission for height system unification starting from a review of the state-of the art of existing height systems, continuing with a summary of the existing methodologies including possible improvements to be implemented, further continuing with the application of these algorithms to the two test regions North America and Europe and the ocean in between, and finalizing with an assessment of the impact of GOCE in these test areas. As outcome of the study a list of recommendations for the realization of globally consistent and accurate height systems is formulated addressing specifically different situations related to terrestrial data coverage and applications. Worldwide more than 100 height systems exist. Most of them refer to an adopted value of mean sea level at a reference marker. The connection of height systems located on one continent is straightforward in principle; it is done by geodetic levelling in combination with gravimetry. Height systems separated by sea cannot be unified in this manner and the height offsets between their reference markers are unknown. They do not refer to one common level (i.e., equipotential) surface. In essence, this project demonstrated how GOCE will allow computing gravity potential differences (or corresponding differences in physical heights) between arbitrary points on the Earth’s surface with accuracy of 0.1-0.2 m2/s2 (corresponding to 1-2 cm in terms of physical heights). Applying the basic approximate relation, where H is a physical, h an ellipsoidal and N is the geoid height, one can convert between geometrical heights h, as determined with GNNS and physical heights H, as derived from geodetic levelling combined with gravimetry, if one knows the geoid height with sufficient accuracy. As an example of results, this project also contributed to solve a long-lasting controversy among scientists. For decades, scientists have disagreed about whether the sea is higher or lower heading north along the east coast of North America. Thanks to precision gravity data from ESA’s GOCE satellite, this controversial issue has now been settled. The answer? It’s lower. Until recently, geodesists thought that the height of the sea increased with latitude along the Atlantic coast from Florida to Canada. Their conclusions, which go back to the 1920s, were based on traditional methods that connect values of mean sea level from tide gauge measurements. Scientists from the GOCE+ HSU project team used the GOCE geoid to determine a reference level surface. This allows the unification of different national height systems providing a solution to this long debate.