If you had billions of dollars to make the world a better place, and could spend it however you wanted, how would you maximize your impact? This is not just a thought experiment, but a daily concern for the world’s governments, philanthropists, and multilateral institutions. Since 2004, Copenhagen Consensus has been using cost-benefit analysis to help decision makers identify highly effective interventions. While most cost-benefit analysis seeks the best solution for a single problem, Copenhagen Consensus takes a wider view, looking across all major domains for policies that improve social welfare.