Data capture, processing, analysis and archiving is central to scientific endeavour, challenging the sustainability of an approach to ICT deployment that has predominated for 25 years but is rapidly being overtaken by events. Cloud-based services offer greater efficiency, agility and innovation in delivery of services through economies of scale, multiple tenancy of irregularly-used resources and more sophisticated approaches to resource management.We estimate that cloud-based services to the ERA communities could become a €bn business in the near future. Efficiency savings of just 10% would equate to something like 40% of the annual (2002-2013) INFRASTRUCTURES budget. This is of great significance to suppliers of cloud-based services and national and European funding agencies as well as infrastructure operators.The HELIX NEBULA Project is a preliminary step towards a European cloud-based scientific e-infrastructure: HELIX NEBULA – the Science Cloud. The Science Cloud Strategic Plan was adopted by representatives of all three stakeholder groups, including a representative from the Cabinet of the EU Vice Presidency responsible for the Digital Agenda, at a workshop hosted by ESA/ESRIN in June 2011.The supporters of the HELIX NEBULA initiative include: ATOS, BT Global Services, CAP Gemini, CERN, CloudSigma, CNES, CNR, DLR, the EC, EGI.eu, EMBL, ENEA, ESA, Logica, OpenNebula, Orange Business Services, SAP, SIENA, StratusLab, Server Labs, Six2, T-Systems International, Terradue srl, Thales and TrustIT.The HELIX NEBULA Project will lead and co-ordinate these communities of interest through a two year pilot-phase during which procurement processes and governance issues for a framework of public/private partnership will be appraised. Three flagship use cases from HEP, molecular biology and earth-observation will be used to enable a cost-benefit analysis to be undertaken and the next stage of the Science Cloud Strategic Plan developed and approved.