This book constitutes the refereed proceedings of the 4th European Con ference on Principles and Practice of Knowledge Discovery in Databases , PKDD 2000, held in Lyon, France in September 2000. The 86 revised pa pers included in the book correspond to the 29 oral presentations and 57 posters presented at the conference. They were carefully reviewed a nd selected from 147 submissions. The book offers topical sections on new directions, rules and trees, databases and reward-based learning, classification, association rules and exceptions, instance-based disco very, clustering, and time series analysis.