The goal of the DL.org, Coordination Action on Digital Library Interoperability, Best Practices, and Modelling Foundations, is to create a framework where key representatives from major initiatives and on-going Digital Library related projects may collaborate, discuss experiences, exchange expertise, work on interoperability of their solutions, promote shared standards, and provide the DL community with a deeper understanding of key issues and new directions. The ultimate objective will rapidly advance research and development techniques thus facilitating the creation of a European Information Space. In using the DELOS Digital Library Reference Model as its conceptual and operational basis, the project will be making an innovative attempt to achieve the above and concrete, far-reaching results that will be much broader and have a much more significant impact that any other similar effort in the past. DL.org will be active at a crucial time by executing coordination actions that target the essence of integration amongst a series of many DL efforts that are currently on-going, each one acting in isolation and adopting ad-hoc solutions and methodologies. The main instrument of the project to promote interoperability among all relevant efforts consists of six thematic Working Groups composed by DL.org partners and representatives from prominent DL projects and organisations. Key expected outcomes of DL.org include (i) a “Digital Library Technology and Methodology Cookbook” providing a portfolio of current best practices and patterns to facilitate cross-fertilization between existing systems and their enhancement in terms of critical interoperability issues; (ii) a consolidated and enhanced version of the DELOS Digital Library Reference Model; (iii) workshops, summer schools, eCourses and dissemination activities to communicate the impact of DL.org achievements to relevant communities.