This book constitutes the thoroughly refereed postproceedings of the Third International Workshop on Innovative Internet Community Systems, IICS 2003, held in Leipzig, Germany in June 2003.The 19 revised full papers presented together with 2 invited papers have gone through two rounds of reviewing and improvement and were selected from more than 30 submissions. Among the topics addressed are semantic search, network communities, e-learning, message-oriented middleware, networked information spaces, mobile business processes, distributed communication systems, distributed Web applications, semantic Web environments, file-sharing systems, network intrusion detection, protocols, self-organizing networks, XML, and linguistic knowledge services.