This book constitutes the refereed proceedings of the 21st Conference of the Spanish Association for Artificial Intelligence, CAEPIA 2026, held in Jaén, Spain, during November 11–13, 2026.

The 38 full papers presented in this book were carefully reviewed and selected from 182 submissions. The papers covers such themes as computer vision and robotics; foundational models / LLMs; machine learning; optimization, search and planning; real-world applications; and recommender systems.