New assessment system for buildings known as CASBEE (Comprehensive Assessment System for Building Environmental Efficiency) has been developed. In CASBEE, two environmental aspects i.e. environmental load (L) and quality of building performance (Q) are set as the major assessment targets. BEE (Building Environmental Efficiency) is defined as Q/L, following the concept of eco-efficiency. This assessment structure is the most unique point of CASBEE compared with existing assessment tools. With the increasing BEE value, total environmental performance of buildings is labeled as any of Class C (Poor), B-, B+, A, and S (Excellent). CASBEE is going to provide four tools according to the lifecycle of a building.