This book constitutes the refereed proceedings of the 17th Conference on Fuzzy Logic and Intelligent Technologies in Nuclear Science, FLINS 2026, and 21st International Conference on Intelligent Systems and Knowledge Engineering, ISKE 2026, held in Sydney, NSW, Australia, during July 15-19, 2026. The 152 full papers and 8 short papers presented in this book were carefully selected and reviewed from 275 submissions. These papers have been organized in the following topical sections: Part I: Fuzzy Machine Learning and Decision Making Part II: Knowledge Engineering, LLMs, and Reasoning Part III: Computer Vision and Medical Imaging Part IV: Graph Neural Networks and Relational Intelligence Part V: Trustworthy, Federated, and Robust Learning Systems