Thoroughly refereed post-proceedings of the 5th International Workshop on Innovative Internet Community Systems, IICS 2005, held in Paris, France, in June 2005. The 17 revised full papers presented have been carefully reviewed and selected from 27 submissions. They mainly address system-oriented problems, content and text processing, and theoretical foundations of quality-of-service problems of Internet protocols, aspects of cooperation and collaboration in Internet systems, as well as agent and text-processing-based methods.