The papers in this volume are the refereed technical papers presented at AI-2006, the Twenty-sixth SGAI International Conference on Innovative Techniques and Applications of Artificial Intelligence, held in Cambridge in December 2006. They present new and innovative developments in the field, divided into sections on AI Techniques, Knowledge Discovery in Data, Argumentation, Dialogue Games and Optimisation, Knowledge Representation and Management, Semantic Web, and Model Based Systems and Simulation. For the first time the volume also includes the text of short papers presented as posters at the conference. This is the twenty-third volume in the Research and Development series. The series is essential reading for those who wish to keep up to date with developments in this important field. The Application Stream papers are published as a companion volume under the title Applications and Innovations in Intelligent Systems XIV.