Mission and vision of the project are to be a core contributor to European Open Science Cloud service portfolio, commit to EOSC governance and ensure inclusiveness on the European level. The objective of the project is to support the development and inclusion of the national Open Science Cloud initiatives in 15 Member States and Associated Countries in the overall scheme of EOSC governance; spread the EOSC and FAIR principles in the community and train it; and provide technical and policy support in on-boarding of the existing and future service providers into EOSC, including generic services (compute, data storage, data management), thematic services, repositories and data sets - thus covering the whole spectrum of services related to Open Science, data and publications. The overall approach is that national Open Science landscape in all countries will be mapped, analysed and systematized so as to facilitate both the creation of national OSC initiatives to support the overall EOSC governance, and to engage all stakeholders. A set of providers (generic e-Infrastructure providers, thematic providers, repositories) will be on-boarded into EOSC - following the best practices, policies, guidelines and tools formulated by the project, in alignment with the existing EOSC initiatives and standards. The project solutions provided will be interoperable with EOSC services and will be tested and fine-tuned by real users, and the widest community will be supported in the uptake of research data sharing and practices, in alignment with FAIR principles. Following the work programme requirements, the project will support the operational framework for governance by focusing on coordination between relevant national initiatives, as well as data infrastructures, e-Infrastructures and thematic services, and their federation into the EOSC. The effort is mandated by national governments of 15 countries through explicit Letters of Support.