Through C40’s Private Building Efficiency Network, cities work together to improve the energy efficiency of existing commercial and residential buildings. In 2014 several cities, led by Tokyo, developed the report Urban Efficiency: a global survey of building energy efficiency policies in cities. The report incorporated best practices from around the world, including financial incentives, sectoral benchmarking, and building optimisation programmes into city energy plans and roadmaps. Other cities used it as an evidence base to push for the introduction of new, ambitious building energy policies or expand already successful schemes. We hope the next instalment of this report will prove just as valuable.