This book constitutes the refereed proceedings of the 34th International Conference on Case-Based Reasoning Research and Development, ICCBR 2026, held in Bremen, Germany, during August 13–16, 2026.The 36 full papers included in this book were carefully reviewed and selected from 85 submissions. They were organized in topical sections as follows: Foundations, Retrieval, and the State of CBR; Explainable, Multimodal, and Responsible CBR; LLM-Based CBR: Prompting, Adaptation, and Generation; CBR for Dynamic Real-World Domains and Applications; Security, Workflows, and CBR Development;