MESEO aims to design, prototype and demonstrate an open, flexible and scalable multi-mission EO End-to-End system for massive processing. It will improve performance bottlenecks either on board or on ground while ensuring Space data sovereignty. The main goal of the proposed approach is to improve quality of service and timeline reactivity by improving the End-to-End EO chain at different levels and processing edges while reducing communication bandwidth and incorporating new technology optimised in power consumption and processing capabilities. MESEO will promote a collaborative digital ecosystem enabled by an EO Coordinator Centre together with distributed and heterogeneous Processing Functions. Those Functions will be exported through harmonized interfaces which will ensure the data sovereignty. EO ecosystem players will register their products/services as exported Functions into the ecosystem. The EO Coordinator Centre will control which registered Processing Function to activate in a transparent manner for optimal End-to-End performance, from either timing or quality point of view, for a given End-User request. MESEO specifically addressed both upstream and downstream parts of the EO data processing value chain in a transparent manner. Performance enhancements analysis will tackle major bottlenecks on each link of the EO data processing running either on board or on ground. MESEO proposed innovations will address such bottlenecks. Green Deal related pilot applications (methane monitoring and crops classification) will serve to demonstrate the performance enhancements due to the proposed innovations.