Knowledge Discovery in Databases: PKDD 2004 : 8th European Conference on Principles and Practice of Knowledge Discovery in Databases Pisa Italy September 20 24 2004. Proceedings This book constitutes the refereed proceedings of the 8th European Conference on Principles and Practice of Knowledge Discovery in Databases PKDD 2004 held in Pisa Italy in September 2004 jointly with ECML 2004. The 39 revised full papers and 9 revised short papers presented together with abstracts of 5 invited talks were carefully reviewed and selected from 194 papers submitted to PKDD and 107 papers submitted to both PKDD and ECML. The papers present a wealth of new results in knowledge discovery in databases and address all current issues in the area