This book constitutes the refereed post proceedings of the 19th International Conference on Advances in Computer Games, ACG 2025, held online, during October 21–23, 2025.The 17 full papers included in this book were carefully reviewed and selected from 30 submissions. They were organized in topical sections as follows: Game Solvers, Engagement and Fairness, Large Language Models, Learning and Tree Search, Human Gameplay, Imperfect Information Games.