The 3rd Workshop on Foundations of Digital Libraries was held in Århus, Denmark, on September 18, 2008, in conjunctions with the 12th European Conference on Research and Advanced Technologies on Digital Libraries (ECDL2008). Like the two previous workshops in the series, it was dedicated to discussing several fundamental issues of Digital Libraries (DLs) related to modelling the key concepts that characterise the field. In particular, it focused on problems related to interoperability in large federated Digital Libraries. Experts participating in prominent DL projects were invited to present the main interoperability problems identified in their domain, the solutions applied, and the main open issues. The DELOS Reference Model for Digital Libraries was suggested as the conceptual tool to be used as a formal basis for understanding and discussing the full spectrum of interoperability issues. View online