The Global Geodetic Observing System (GGOS) provides measurements of the time varying gravity, rotation, and shape of the Earth using instruments located on the ground and in space. These measurements need to be accurate to better than a part per billion in order to advance our understanding of the underlying processes that are causing the Earth's rotation, gravity, and shape to change. Mass transport in the global water cycle, sea level change, and crustal deformation associated with geohazards are examples of particularly demanding applications of geodetic measurement systems. Designing the ground- and space-based instruments that are needed to provide geodetic measurements of the accuracy and stability required for these and other applications are an ongoing challenge for GGOS. This session will be a forum for discussing demanding scientific applications of global geodetic measurement systems and the ground- and space-based infrastructure that is needed to fulfill those demands.