Retaining all the key features of its predecessors, this fifth edition of a long-established, bestselling text explores the principal topics of mathematical logic. It includes a new section covering basic ideas and results about nonstandard models of number theory, a second appendix that introduces modal propositional logic, an expanded bibliography, and additional exercises and selected answers. This edition continues to cover propositional logic, first-order logic, first-order number theory, axiomatic set theory, and the theory of computability. It also discusses the major results of Gödel, Church, Kleene, Rosser, and Turing.