Policymakers and the public have been concerned about the effects of media violence on children for decades. Scientific psychological research can be an important source of information for policy, as the goal of science is to separate facts from opinions. This article reviews children's exposure to media violence, describes theories that explain the effects media violence could have, summarizes the research on the effects of media violence exposure, and describes several moderators that can enhance or mitigate those effects. These scientific findings provide useful information for public policy, yet there are many barriers to their use, including misunderstandings of how causality is determined in scientific and public health circles and how large the effects are. Finally, the implications for public policy are discussed, including what has and has not worked in the United States, what other countries and the international community are doing, and where opportunities for new approaches for effective policies may exist.