As highlighted by European Commission in its Digital Agenda, interoperability is a key challenge for developing a sustainable cloud ecosystem in Europe.The European Commission and European national states are investing millions of Euros in collaborative research initiatives bringing the most brilliant minds to address the several challenges cloud computing poses to the EU economy. However, often the short duration of research projects and the lack of tangible support and vehicles for concretely implementing results limit the overall positive impact of all these research projects, hindering their positive outcomes and ultimately those of EC.The fundamental goal of OCEAN is to foster the emergence of a sustainable open source cloud ecosystem and boost market innovation in Europe, by generating greater efficiency and economies of scale among collaborative research projects on open source cloud computing. OCEAN is addressing European FP7 projects funded under the Objective ICT-2011.1.2 as well as other European, European national and Japanese open cloud collaborative projects.OCEAN is to play a pivotal role among collaborative cloud research projects, especially those that are naturally following an open source approach, to help reveal commonalities, being either potential overlapping and/or opportunities for collaboration and synergies. The OCEAN project is launched in order to provide the following results:- Identify current collaborative projects developing open cloud components among European FP7 research projects, other European national research projects, Japanese research projects and register them together with other open cloud projects in an online Open Cloud Innovation Directory.- Provide a relative positioning or functional mapping of these projects, in relation with key standards and reference models provided by leading standard defining organizations such as NIST, ETSI, DMTF, OGF, etc in what we call a Open Cloud Interoperability Framework and Roadmap.- Pre-test and review software artefacts from some open cloud projects and provide online services enabling open cloud projects to build and test their software.- Foster cooperation and integration between projects through the organization of two annual events called "Plugfests" that will provide project teams the appropriate environment to work on the integration and interoperability of their software.- Foster collaboration between European and Japanese entities on open cloud computing, cloud interoperability and standardisation by involving them in the organised Plugfests and in discussions on the Open Cloud Interoperability Framework and Roadmap.Europe as a whole needs projects such as OCEAN to ensure that the European Commission realizes its overarching vision. Only by closing gaps, eliminating overlaps, and avoiding missed opportunities amongst current projects will Europe be able to truly do its best at creating a unique, sustainable open cloud ecosystem.