This book constitutes the thoroughly refereed postproceedings of the 3rd and the 4th International Workshop on Databases, Information Systems and Peer-to-Peer Computing, DBISP2P 2005 and DBISP2P 2006, held in Trondheim, Norway, in August 2005 and in Seoul, Korea, in September 2006, as satellite events of VLDB, the International Conference on Very Large Data Bases.

The 39 revised full papers presented together with 1 invited contribution were carefully selected during two rounds of reviewing and improvement. According to the sessions held in the two editions, the papers of DBISP2P 2005 are organized in topical sections on knowledge discovery and emergent semantics, query answering and overlay communities, indexing, caching and replication techniques, complex query processing and routing, semantic overlay networks, services, agents and communities of interest. The papers of DBISP2P 2006 are thematically divided into data placement and searching, semantic search, query processing and workload balancing, as well as continuous queries and P2P computing.