The NASA and ESA space agencies established the Interagency Gravity Science Working Group (IGSWG) in 2013 to advise on future gravity mission concepts. Both NASA and ESA acknowledge the need for continued global observation of mass transport. Observing mass transport with the highest possible accuracy and spatial resolution and with temporal resolutions from daily to 33 monthly is crucial for understanding the functioning and evolution of the Earth system (climate, geohazards, water cycle). Improved observation of global mass transport in terms of temporal and spatial resolution would benefit a diversity of Earth science domains (e.g. hydrology, oceanography, cryospheric sciences, solid Earth sciences, atmospheric sciences) for both scientific and application focused users, and are necessary to fully characterize diverse global change processes. The working group finalized its activities in 2016 by delivering a report with the title "Towards a sustained observing system for mass transport to understand global change and to benefit society". This report addresses the compatibility between user requirements, constellation concepts, and expected performance. In addition, a roadmap for implementation in the post-2020 time frame is included. This roadmap defines the path towards sustained observation of mass transport with the required accuracy and spatio-temporal resolution, while addressing the need for cooperation between different space agencies and/or providers, and assessing required activities such as studies and technological developments for both the near and longer terms. Coordinators ESA and NASA John Labreque, Thomas Johnson, Ben Phillips (NASA) Roger Haagmans, Luca Massotti, Christian Siemes (ESA) @en