Description DL.org has increased awareness and understanding of interoperability of digital libraries systems and produced an enhanced and consolidated version of the DELOS Reference Model.The goal of the DL.org Coordination Action on Digital Library Interoperability, Best Practices, and Modelling Foundations was to create a framework where key representatives from major initiatives and on-going Digital Library related projects could 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.In using the DELOS Digital Library Reference Model as its conceptual and operational basis, DL.org made an innovative attempt to achieve the above. The main instrument of the project consisted of six thematic Working Groups composed by DL.org partners and representatives from important DL projects and organisations in order to achieve a maximum impact on the digital libraries community and beyond.The main outcomes of DL.org are: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; a consolidated and enhanced version of the DELOS Digital Library Reference Model; workshops, summer schools, eCourses and dissemination activities to communicate the impact of DL.org achievements to relevant communities.