This book constitutes the proceedings of the 31st International Conference on Case-Based Reasoning Research and Development, ICCBR 2023, which took place in Aberdeen, UK, in July 2023. The 26 full papers included in this book were carefully reviewed and selected from 79 submissions. The papers have been organized in topical sections as follows: CBR and deep learning; representation and similarity; CBR and explainable AI; case base maintenance; adaptation: techniques and application; and case-based applications.