The European Middleware Initiative is a collaboration of the three major middleware providers in Europe, ARC, gLite and UNICORE, and other consortia. EMI aims to deliver a consolidated set of middleware components for deployment in EGI, PRACE and other DCIs; extend the interoperability between grids and other computing infrastructures; strengthen the reliability of the services; and establish a sustainable model to maintain and evolve the middleware, fulfilling the requirements of the user communities.European scientific research has benefited recently from the increasing availability of computing and data infrastructures with unprecedented capabilities for large scale distributed initiatives. These infrastructures are largely defined by enabling middleware. After the necessary initial period of research and consolidation that has taken place in the past several years, the growing usage of these resources now requires the transformation of the computing infrastructures into a professionally managed and standardized service. It is of strategic importance for the establishment of permanent, sustainable research infrastructures to lower the technological barriers still preventing resource owners from federating the resources, and potential communities of tens of thousands of researchers from using grids as a commodity tool in their daily activities.The EMI project will make the realization of this vision possible by addressing a number of problems that still prevent users from easily accessing and using the whole capacity of the existing computing infrastructures. It will focus on improving the usability and accessibility for scientific users and the interoperability and manageability for service providers. The sustainability of the grid services will be directly addressed by replacing wherever possible proprietary technology with off-the-shelf components, improving their standardization and implementing industry standard quality assurance methodologies.