This book constitutes the thoroughly refereed postproceedings of the 4th International Workshop on Innovative Internet Community Systems, IICS 2004, held in Guadalajara, Mexico, in June 2004. The 25 revised full papers presented together with 2 invited papers have been carefully reviewed. They focus mainly on system-oriented problems, text processing, and theoretical foundations of distributed and Internet systems. They also deal with speed and quality-of-service problems of Internet protocols, aspects of cooperation and collaboration in Internet systems, as well as agent and text-processing-based methods. In addition, 9 papers stem from two mini-workshops, one on computational epidemiology and the other on optimization of urban traffic systems.