This book constitutes the refereed proceedings of the 12th International Conference on Artificial Intelligence: Methodology, Systems, and Applications, AIMSA 2006. The 28 revised full papers presented together with the abstracts of 2 invited lectures were carefully reviewed and selected from 81 submissions. The papers are organized in topical sections on agents, constraints and optimization, user concerns, decision support, models and ontologies, machine learning, ontology manipulation, natural language processing, and applications.