This paper provides a global overview of the design, implementation, and evolution of building energy codes. Reflecting alternative policy goals, building energy codes differ significantly across the United States, the European Union, and China. This review uncovers numerous innovative practices including greenhouse gas emissions caps per square meter of building space, energy performance certificates with retrofit recommendations, and inclusion of renewable energy to achieve 'nearly zero-energy buildings'. These innovations motivated an assessment of an aggressive commercial building code applied to all US states, requiring both new construction and buildings with major modifications to comply with the latest version of the ASHRAE 90.1 Standards. Using the National Energy Modeling System (NEMS), we estimate that by 2035, such building codes in the United States could reduce energy for space heating, cooling, water heating, and lighting in commercial buildings by 16%, 15%, 20%, and 5%, respectively. Impacts on different fuels and building types, energy rates and bills as well as pollution emission reductions are also examined. decade, growing by 37.5 million m 2 . 2 With the bulk of this expansion anticipated to occur in developing countries, building-related policies will be important in managing future energy consumption and greenhouse gas emissions. The International Energy Agency (IEA) predicts that countries in the Organization for Economic Co-operation and Development (OECD) will have a construction rate of about 1% annually. Meanwhile, the building stock in major non-OECD countries is expected to expand 5-10% annually over the next two decades. 3 Commercial buildings are increasing in relative importance, representing a larger share of floor space and energy consumption in the world. 2 In OECD countries, these buildings consumed about 32.2% of total electricity and 13.4% of total primary energy in 2012. 4 While commercial buildings' share of total energy consumption is relatively small in China today (representing only 5.3% of its electricity 188