DANUBIUS-PP is a three-year project to raise DANUBIUS-RI (International Centre for Advanced Studies on River-Sea Systems) to the legal, financial and technical maturity required for successful implementation and development. DANUBIUS-RI is a pan-European distributed research infrastructure (RI) building on existing expertise to support interdisciplinary research on river-sea (RS) systems, spanning the environmental, social and economic sciences. It will provide access to a range of RS systems, facilities and expertise, a ‘one-stop shop’ for knowledge exchange, access to harmonised data, and a platform for interdisciplinary research, education and training. DANUBIUS-PP will bring together key stakeholders at different levels and strengthen the consortium through a process of wide engagement. Individual work packages will refine, inter alia, the scientific and innovation agenda, the legal framework, governance and management, and policies for access and data management. The financial requirements of the RI will be refined to assist funding agencies as they consider future spending priorities. Key deliverables of DANUBIUS-PP include development of the legal and financial agreements for the components of the RI (including Hub, Nodes and Supersites), their governance, and internal organisation which will be confirmed via a Memorandum of Understanding. This preparatory phase project will develop the structures and processes to ensure that the RI strengthens scientific performance by providing a sustainable basis for future operation, delivering key services to the different user communities.