Plagiarism in computer science courses has become increasingly widespread. This paper describes the approach taken at Stanford University over the past ten years in an attempt to control this problem. Our approach consists of five steps. First, we have encouraged computer science faculty to become actively engaged in the university judicial process. Second, we have instituted the practice of using "expert witnesses" who are familiar with programming assignments as part of the judicial process. Third, we have redefined the most common violation-one student who copies an assignment from another-as "plagiarism" instead of "unpermitted collaboration." Fourth, we have adopted electronic tools to detect instances of such plagiarism. Fifth, we have established explicit departmental policies about collaboration and plagiarism and made sure that those policies are well understood by students. By adopting this multifaceted approach, the computer science department has been able to detect a larger fraction of the instances of academic dishonesty and prosecute more effectively the violations that occur.