Newer computingareas like peer-to-peer,grid, and service-orientedcomputing provide a number of opportunities and challenges for architectures of future digital libraries. Peer-to-peer data management allows for loosely coupled integration of information services and sharing of information such as recommendations and annotations. Grid computing middleware is needed because certain services within digital libraries are complex and computationally intensive, e.g., extraction of features in multimedia d- uments to support content-based similarity search or for information mining in b- medical data. The service-orientation provides mechanisms to describe the semantics and usage of information services and to combine services into work?ow processes for sophisticated search and maintenance of dependencies. Elements of all three directions should be combined in a synthesis for future digital libraries architectures. This volume contains selected and revised papers from the Sixth Thematic Wo- shop of the EU Network of ExcellenceDELOS on Digital Library Architectures,which washeldin S. MargheritadiPula (Cagliari),Italy,24-25June2004.Thisworkshopwas co-located with the 12th Italian Symposium on Advanced Database Systems (SEBD 2004) and organizedjointly by the DELOS Network of Excellence and the Department ofInformationEngineeringoftheUniversityofPadua,Italy.DELOS(http://www.delos.