This book is a rigorous introduction to classical and nonclassical logics which emphasizes deduction as a form of computation. It can be used to teach classical, modal, and intuitistic predicate logic. It also presents the logical and mathematical foundations for resolution theorem proving and Logic Programming. A distinctive feature of this book is its uniform mathematical treatment of logic, based on the tableau method of classical logic, which includes soundness, completeness, compactness, incompleteness, and the theorems of Herb Rand and Skolem-L Wenheim. The same uniform treatment is used for important areas of application in computer science and artificial intelligence. These include resolution theorem proving, Logic Programming and Prolog, Predicate Intuitionistic Logic, and Predicate Modal Logic. There is also an historical appendix and an extensive list of selected references so that both the background and more advanced developments of these subjects can be understood and pursued. This text is appropriate for upper level undergraduate and beginning graduate students.