The adoption in 2015 of the Paris Agreement and the United Nations 2030 Agenda, with its Sustainable Development Goals, marked a turning point: policies for fossil fuel subsidies (FFSs) need to radically change. The G20 countries are contributing to this effort through peer reviews on FFSs: the peer review mechanism highlights the importance of transparency and accountability in this domain. FFSs cause excessive consumption of fossil fuels, exacerbate environmental pollution, result in lost government income and provoke serious health damages. Moreover, FFSs are inefficient from both an environmental and an economic point of view. They may be efficient on social grounds; but experience and analysis show that direct subsidies for poor and vulnerable groups are more efficient and avoid sending the wrong price signals to the market. This chapter describes the origins, process and results of the first G20 peer reviews (China-US; Mexico-Germany; and Indonesia-Italy).