Science is a creative process where the synthesis of new ideas requires discussion and debate. However, the traditional model for teaching assumes that all information presented to students is automatically learned. As a result, most students leave their introductory science courses frustrated and without a solid conceptual understanding. At the same time, instructors feel that students have not lived up to their expectations, yet they cannot identify the problem. Peer Instruction is an interactive approach that was designed to improve the learning process. This approach provides students with greater opportunity for synthesizing the concepts while instructors get timely feedback that can help focus the instruction on the points that are the most difficult for the students. Peer Instruction is flexible and easy to use on its own or in conjunction with other teaching methods. This chapter discusses the motivation for using Peer Instruction and the mechanics of implementing it in the classroom.