This volume reports the proceedings of the 15th Italian Workshop on Neural Nets WIRN04. The workshop, held in Perugia from September 14th to 17th 2004 has been jointly organized by the International Institute for Advanced Scienti?c Studies "Eduardo R. Caianiello" (IIASS) and the Societ' a Italiana Reti Neuroniche (SIREN). This year the Conference has constituted a joint event of three associations: Associazione Italiana per l'Intelligenza Arti?ciale (AIIA), Gruppo Italiano di Ricercatori in Pattern Recognition (GIRPR), Societ' a Italiana Reti Neuroniche (SIREN) within the conference CISI-04 (Conferenza Italiana sui Sistemi Int- ligenti - 2004) combining the three associations' annual meetings. The aim was to examine Intelligent Systems as a joint topic, pointing out synergies and d- ferences between the various approaches. The volume covers this matter from the Neural Networks and related ?elds perspective. It contains invited review papers and selected original contri- tions presented in either oral or poster sessions by both Italian and foreign - searchers. The contributions have been assembled, for reading convenience, into ?ve sections. The ?rst two collect papers from pre-WIRN workshops focused on Computational Intelligence Methods for Bioinformatics and Biostatistics, and Computational Intelligence on Hardware, respectively. The remaining sections concern Architectures and Algorithms, Models, and Applications. The Editors would like to thank the invited speakers and all the contributors whosehighlyquali?edpapershelpedthesuccessoftheWorkshop.Finally,special thanks go to the referees for their accurate work.