The IAG’s Global Geodetic Observing System (GGOS) provides the fundamental ground- and space-based geodetic observations needed to improve our understanding of the Earth’s variable shape, rotation, and gravity. GGOS is forming a comprehensive geodetic observing instrument that unifies and integrates the hitherto separate pillars of geodesy (shape, rotation, and gravity) into one consistent observing system. GGOS is also pursuing the unification of existing local height systems into a global world height system. This session is a forum for discussing past, present, and future geodetic observing networks, the integration of the technique-specific observing networks into a unified geodetic observing system, and the use of the system for improving our understanding of the dynamic Earth. Presentations are particularly sought on the creation of a unified height system, including progress and plans towards establishing a global vertical reference equipotential surface and a vertical datum based upon a gravimetric geoid.