This is the first in the series of 10 guidance notes under the Energy Sector Reform Assessment Framework (ESRAF), an initiative of the Energy Sector Management Assistance Program (ESMAP) of the World Bank. ESRAF proposes a guide to analyzing energy subsidies, the impacts of subsidies and their reforms, and the political context for reform in developing countries. This note provides guidance on how to approach and assess energy subsidies, quantifying them where possible. it suggests a definition of subsidies and describes options for categorizing and measuring subsidies. it also outlines policy issues to consider in reforming the subsidies in developing countries.