An Introduction to Mechanics, commonly referred to as Kleppner and Kolenkow, is an undergraduate level textbook on classical mechanics coauthored by physicists Daniel Kleppner and Robert J. Kolenkow. It originated as the textbook for a one- semester mechanics course at the Massachusetts Institute of Technology, where both Kleppner and Kolenkow taught, intended to go deeper than an ordinary first year course. Since its introduction, it has expanded its reach to other universities to become one of the most popular mechanics textbooks.