Estimated at USD 478 billion in 2019, fossil fuel subsidies strain the public purse, contribute to climate change, slow the uptake of renewable energy, and lead to local air pollution and associated impacts on public health. Their reform could thus lead to a wide range of socioeconomic and environmental benefits. Despite its binding rules to regulate subsidies, the World Trade Organization (WTO) has so far failed to play any significant role in constraining government support to fossil fuels. Against this backdrop, this report explores whether WTO rules and practices are fit for purpose in addressing fossil fuels subsidies and supporting the clean energy transition, and how they could be reformed to more effectively contribute to these key objectives. It also offers practical recommendations for WTO members and other stakeholders interested in moving this agenda forward.