This book constitutes the refereed proceedings of the 9th Dortmund Fuzzy Days, held in Dortmund, Germany, 2006. The Fuzzy Days conference has established itself as an international forum for the discussion of new results in the field of Computational Intelligence. All the papers had to undergo a thorough review guaranteeing a solid quality of the programme. The papers are devoted to foundational and practical issues in fuzzy systems, neural networks, evolutionary algorithms, and machine learning and thus cover the whole range of computational intelligence. Included also is the chapter "Use of Variable Fuzzy Sets Methods for Desertification Evaluation" (by Wu Li, Guo Yu, Chen Shouyu, and Zhou Huicheng)