Conducting city assessments and disclosing those results to the public is important for supporting citizens' understanding of the actual condition of their city. Such assessment and disclosure could introduce a market mechanism that can be expected to provide city governments with strong incentives to improve their city conditions and also recognizes that local policy and strategy can be the most appropriate way to address specific urban and environmental problems. The latest Comprehensive Assessment System for Built Environment Efficiency (CASBEE) tool, referred to as CASBEE-City, is presented. Designed specifically for city assessment, it supports local governments and other stakeholders in identifying the environmental, social and economic characteristics of their city and in quantifying the effectiveness of their city-wide policies. CASBEE-City is based on the concept of environmental efficiency and it provides a combined evaluation of a city embracing two aspects: the environmental load imposed by the city on the wider environment outside its boundary, and the quality of life (environmental, social, economic) inside the city. A city with low environmental load and high quality receives a high Built Environment Efficiency (BEE) value and is regarded as a sustainable city within the CASBEE framework.