This book constitutes the proceedings of the 18th International Conference on Brain Informatics, BI 2025, which was held in Bari, Italy, during December 11–13, 2025. The 45 full papers included in this book were carefully reviewed and selected from 129 submissions. They were organized in topical sections as follows: Cognitive and Computational Foundations of Brain Science; Investigations of Human Information Processing Systems; Brain Big Data Analytics, Curation and Management; Informatics Paradigms for Brain and Mental Health Research; Brain-Machine Intelligence and Brain-Inspired Computing; Brain Informatics 2025 Workshop on Web Intelligence meets Brain Informatics; The 4th Workshop on Environmental Adaptation and Mental Health; The International Workshop on Brain Information Mechanisms in Special Populations; The International Workshop on Neural Data Analysis for Brain-Computer Interfaces and Brain Disorders; The Special Session on Spatio-Temporal Brain Data Modelling: New Approaches to Understanding Brain Dynamics.