Supersites are the components of the DANUBIUS-RI distributed Research Infrastructure which will be the test beds of the DANUBIUS-RI scientifically excellent ideas, areas where the developed concepts will be refined and verified. They will provide natural laboratories for observation, research, modelling and innovation at locations of high scientific importance and opportunity, covering RS systems from river source to transitional waters and coastal seas. Ranging from the near pristine to the heavily impacted, the Supersites will be selected to provide contrasting systems across environmental, social and economic gradients that have been impacted, to varying degrees either directly or indirectly, by industrialisation, urbanisation, population expansion, land use change and farming. They will provide interdisciplinary research platforms and identify, model and define system states and conditions for naturally and anthropogenically triggered transitions in the physical, biogeochemical and biological states. They will provide excellent opportunities to undertake social and economic investigations in contrasting settings.