The future and security of humankind dwelling on Planet Earth depend on our ability to live and cope with the complex Earth system in all its dimensions. Our ability to monitor the surface and subsurface of the Earth and to forecast catastrophic events and their impacts on society is increasingly pertinent as our society develops. Earth system processes transcend national boundaries and the European Plate Observing System (EPOS) brings the solid Earth networks in Europe into a single distributed research infrastructure. EPOS has been designed with the vision and the mission of creating a pan-European infrastructure for solid Earth science relying on novel e-science concepts to provide virtual access to data and services as well as physical access to facilities for a broad community of users. The innovation potential of the EPOS infrastructure involves enabling the use of multidisciplinary solid Earth science data, data products and services relying on national research infrastructures distributed across the whole Europe. The overall objective of the EPOS Sustainability Phase (EPOS SP) project is to ensure the long-term sustainability of the EPOS Research Infrastructure. This will be done by creating effective synergies among diverse actions dedicated to: (i) secure governance and financial sustainability through the entire research infrastructure lifecycle; (ii) secure technical sustainability and develop innovation to fully exploit data and service provision; (iii) establish and maintain excellence by preserving and reinforcing the trust and awareness of users; (iv) exploit economic and societal benefits to keep stakeholders engaged. The EPOS SP project is timely in the EPOS RI lifecycle because it will consolidate the long-term operational perspective of EPOS ERIC and the EPOS Delivery Framework. EPOS SP is addressing all aspects of sustainability to tackle the challenge of moving from technical and financial viability to long-term sustainability.