The Collaborative and Sustainable Astronomical Data Infrastructure for Europe (CoSADIE) project will undertake actions aimed at designing a sustainable version of the already successful European Virtual Observatory (Euro-VO). The concept of a Virtual Observatory (VObs or VO) is that all the world's astronomical data should feel like they sit on the astronomer's desktop workspace, analysable with a user selected workbench of tools and made available through standard interfaces across the whole range of astronomical research topics. VObs is embraced as a world-wide community-based initiative with the potential to transform and restructure the way astronomy research is done. The European Virtual Observatory, Euro-VO, is the European implementation of this idea. The astronomical Virtual Observatory has been identified as one of the important infrastructures of astronomy in the recent European strategic exercise performed by the Astronet ERA-NET. The VObs is currently in transition towards operational phase. This proposal is centred on the development of strategies and coordination structures, through a feasibility study for a sustainable European Virtual Observatory giving access to the open, highly diverse, highly distributed data holdings of astronomy. It also aims at disseminating results among and gathering requirements from the scientific community (users) and the data providers. It will co-ordinate European technical activities, and includes the promotion and monitoring of international standards, and their adoption through the International Virtual Observatory Alliance. Co-operation and interface with the grid and cloud will also be assessed, with a particular consideration towards EGI.eu and OGF. Specific care will be taken to consolidate the high impact VObs outreach activities towards education and the general public.