A Guide to the Methodology of Estimating Transport Emissions Inventories and the Associated Social Cost. The Transport Emissions & Social Cost Assessment is a project under the World Resources Institute’s Sustainable and Livable Cities Program, funded by the Caterpillar Foundation. The project aims to develop a methodology guide, with a simple MS Excel– based tool, to estimate transport emissions inventories and evaluate the associated social impact costs. The scope of the guide and tool covers six air pollutants (NOX, SOX, PM2.5, PM10, CO, and HC) and three GHGs (CO2, CH4, and N2O) for 18 types of transport modes at either the national or city level, specifically for the regions with limited data accessibility and weak data quality. With the methodology of social cost evaluation, the guide and tool can help with more cost-efficient policy-making.