Synopsis This volume consists of eighteen new essays, written by distinguished scholars, on topics that are of great interest to logicians and philosophers: definitions and the concept of truth. The essays fall into three groups. The first group defends the logical legitimacy and fruitfulness of circular definitions. It argues that circular definitions yield better theories not only of truth but also of defeasible inference, rationality, knowledge, and vagueness. The second group contributes to the philosophical debate over deflationism. The final group is concerned with recent logical theories of truth. This group includes critical assessments of fixed point and revision theories. It includes also new and accessible presentations of pointer semantics theory by their originators.