How do you motivate students to do their homework? Some instructors make students' homework scores a significant percentage of the final course grade. In that case, how much course credit is required? Some instructors do not grade homework at all, instead relying on students' intrinsic motivation to learn the course material. Will this actually work? Some instructors might motivate students by having quiz and/or exam problems closely match the assigned homework problems. In this article, we report on the effectiveness of grade incentives, homework-based quiz problems, and intrinsic motivation for 16 semesters of introductory mechanics and introductory electricity and magnetism (E&M) courses at the United States Air Force Academy (USAFA) between fall 2008 and spring 2012.