This book constitutes the refereed proceedings of the 4th International Conference on Case-Based Reasoning, ICCBR 2001, held in Vancouver, BC, Canada, in July/August 2001. The 36 revised full research papers and 14 revised full application papers presented together with 3 invited papers were carefully reviewed and selected from 81 submissions. The papers address all current foundational and theoretical aspects of case-based reasoning as well as advanced applications in a variety of fields.