This text presents a self-contained introduction to logic suitable for majors and nonmajors, and can be covered entirely in a one-semester course. Natural deduction systems of sentential logic and of first-order logic, truth tables, and the basic ideas of model theory are presented without superfluous discussion. This allows the instructor to choose various ways of presenting the material. The text is organized into definitions, comments, examples, and exercises in a modern, visually helpful format. Comments are kept to a minimum so that definitions and examples are usually on the same page, making it easy for students to compare the two. In addition, there are over 500 exercises, with solutions to more than half of them provided in an appendix. Logic Primer differs from existing texts in several important ways. The proofs are shorter and more elegant. The rules of proof are stated in terms of denials of sentences rather than negations; this results in more intuitive rules that students learn more quickly. Most important pedagogically, the authors' natural deduction systems explicitly track the assumptions on which each step in a proof depends.