The refereed proceedings of the 5th International Conference on Case-Based Reasoning, ICCBR 2003, held in Trondheim, Norway, in June 2003. The 51 revised full papers presented were carefully reviewed and selected from 92 submissions. All current aspects of CBR are addressed including case representation, similarity retrieval, adaptation, case library maintenance, multi-agent collaborative systems, data mining, soft computing, recommender systems, knowledge management, legal reasoning, software reuse, and music.