This book constitutes the proceedings of the 20th International Conference on Hybrid Artificial Intelligence Systems, HAIS 2025, held in Salamanca, Spain, during October 16–17, 2025.The 53 full papers included in this book were carefully reviewed and selected from 120 submissions. They focus on the following topical sections:Part I: Agricultural and Environmental Monitoring; Biomedical Applications; Cybersecurity and Network Protection; Data Mining and Decision Support Systems.Part II: Deep Learning and Representation Learning; HAIS Energy Applications; Evolutionary Computation and Optimization; Reinforcement Learning and AI Planning; Smart Mobility and Transportation Optimization; Time Series and Forecasting Methods.