This book constitutes the refereed proceedings of the 4th International Conference on Artificial Intelligence for Mental Health, ICAIMH 2026, held in Merida, Mexico, during July 1–3, 2026.The 11 full papers and 4 short papers included in this volume were carefully reviewed and selected from 36 submissions. They are organized into the following topical sections: Physiological Signal Processing; Machine Learning; Applications; Novel AI Approaches; and Large Language Model Applications.