Description:This book constitutes the major results of the EU COST (European Cooperation in the field of Scientific and Technical Research) Action 274: TARSKI - Theory and Applications of Relational Structures as Knowledge Instruments - running from July 2002 to June 2005. The 17 revised full papers were carefully reviewed and selected for presentation. The papers are devoted to further understanding of interdisciplinary issues involving relational reasoning by addressing relational structures and the use of relational methods in applicable object domains such as non-classical logics, multimodal logics and relational logics, binary relation logic, algebraic logic, fuzzy preference relations, lattices, dominance relationship, extending aggregation operators, and various applications.