Countries can choose between a wide range of policy instruments to address climate change. While economists tend to argue for the efficiency of instruments such as environmental taxes, many countries are incorporating subsidies into their plans for limiting greenhouse gas emissions. However, these subsidies may conflict with World Trade Organization rules. This paper analyzes the potential benefits of using climate change subsidies in terms of addressing market failures as well as the risks of protectionism arising from such subsidies. It then examines World Trade Organization rules to determine whether they optimally differentiate between beneficial and harmful subsidy policies. It concludes that existing WTO rules do not provide adequate scope for legitimate subsidies and makes suggestions for reforming subsidies law.