This book constitutes the refereed proceedings of the 12th International Symposium on Integrated Uncertainty in Knowledge Modelling and Decision Making, IUKM 2026, held in hybrid mode in Quy Nhon City, Vietnam, during September 14–17, 2026. The 85 full papers in this book were carefully reviewed and selected from 151 submissions. They were organized in topical sections as follows: Part I: Invited Talks; Machine Learning;Security and Privacy in Machine Learning and Machine Learning Applications Part II: Uncertainty Management and Decision Making; Pattern Recognition and Data Analysis; Language Models and Optimization and Statistical Methods.
