Peer Instruction: A User's Manual is a step-by-step guide for instructors on how to plan and implement Peer Instruction lectures. The teaching methodology is applicable to a variety of introductory science courses (including biology and chemistry). However, the additional material—class-tested, ready-to-use resources, in print and on disk (so professors can reproduce them as handouts or transparencies)—is intended for calculus-based physics courses. Peer Instruction is an interactive teaching style that actively involves students in the learning process by focusing attention on underlying concepts through interactive “ConcepTests,” reading quizzes, and conceptual exam questions. Results, assessed through scores on the Force Concept Inventory and final exams, show that students better understand concepts and perform better on conventional problems in this environment. It can be easily adapted to fit individual lecture styles and used with any textbook. Eric Mazur's Peer Instruction approach has been successfully field-tested in a variety of settings, most of them quite different from his home campus at Harvard University (e.g., University of Massachusetts—Lowell and Appalachian State University).