This book constitutes the refereed proceedings of the 18th International Conference on Artificial General Intelligence, AGI 2025, held in Reykjavic, Iceland in August 2025. The 72 full papers included in this book were carefully reviewed and selected from 179 submissions. They were organized in topical sections as follows: novel learning algorithms, reasoning systems, theoretical neurobiology and bio-inspired systems, quantum computing, theories of machine consciousness, ethics,safety, formal mathematical foundations and philosophy of AGI.