Advance_eLTER marks a crucial step in building the distributed European Research Infrastructure of Long-Term Ecosystem Research sites and socio-ecological research platforms (eLTER RI) to provide highest quality data and services complementary to the European and global environmental RIs. The project will conduct important conceptual work and preparatory steps towards enabling European-scale investigation of the “Critical Zone”, major ecosystems and socio-ecological systems, targeted at supporting knowledge-based decision making at various levels concerning ecosystem services and biodiversity. The review of the eLTER ESFRI proposal submitted by Germany in March 2015 noted the HIGH to VERY HIGH scientific value and necessity of the eLTER RI and was designated as an ‘Emerging’ ESFRI RI. The objectives of Advance_eLTER are firmly anchored in the strategic long-term goals of the eLTER RI, but strictly focus on the challenges identified by the ESFRI review: Detailed design study (WP1), including an in-depth analysis of the scientific questions driving the eLTER RI physical site network design and instrumentation; Prioritization of eLTER services for key user groups (WP2), and a plan for eLTER RI services at all service provider levels (central, cross-site, individual site); Cost analysis and Business plan, for the future eLTER RI operation (WP3); Organisational framework of eLTER RI (WP4), comprising the development of a robust governance scheme, enabling shareholder negotiations and identifying the most suitable legal framework; Consulting, communication and team-building (WP5), advancing the national eLTER ESFRI processes, specifying the role of eLTER in the environmental RI landscape and developing staff capacity for the eLTER ESFRI process. Advance_eLTER will closely cooperate with all LTER related processes and projects and will result in a 2017 eLTER ESFRI proposal.