Effective policies require a good understanding of the setting they aim to regulate. Knowing what are some of the possible unintended consequences can help to plan for them in the policy design stage. Behavioral responses of those that are affected by the policy can reduce its effectiveness, and even result in outcomes that are the opposite of the original goal. In this course, we will review different policies that did not succeed in achieving their intended targets because they did not fully consider what will happen in their aftermath. We will cover policies across a wide range of outcomes: health, energy and environment, development and aid, education, violence reduction, and labor markets. The goal is to understand what went wrong in each case, and to generalize lessons for future policy making. For each policy, we will start with the original problem it was trying to solve, cover some general theory and intuition around its proposed approach, and study a paper that empirically evaluated its impact. No textbook is required for this course. Grading is based on short weekly assignments, a 2-page midterm paper analyzing a currently discussed policy, and a final exam.