Reforming fossil-fuel subsidies is crucial to reducing greenhouse gas emissions and hence meeting climate change goals. Since 2009, G20 leaders have regularly affirmed their joint commitment to rationalise and phase out “inefficient fossil-fuel subsidies that encourage wasteful consumption” over the medium term, while ensuring targeted support for the poorest. The 2020 OECD Inventory of Support Measures for Fossil Fuels documents over 1 300 government budgetary transfers and tax expenditures that support the production and consumption of fossil fuels. This Companion draws on the Inventory’s findings to provide insights on progress in reform.