This book constitutes the refereed proceedings of the 6th International Conference on Case-Based Reasoning, ICCBR 2005, held in Chicago, IL, USA, in August 2005. The 19 revised full research papers and 26 revised poster papers presented together with the abstracts of 3 invited talks were carefully reviewed and selected from 74 submissions. The papers address all current foundational, theoretical and research aspects of case-based reasoning as well as advanced applications either with innovative commercial deployment or practical, social, environmental or economic significance.