Cities are raising their profile within the international energy efficiency arena. More and more cities are committed to become CO2 neutral and engage a low-carbon development transition. At COP23 in Bonn, 25 cities pledged to implement more and more ambitious actions to mitigate and adapt to climate change by 2020. Simultaneously the Global Covenant of Mayors for Climate & Energy has formulated a global standard on cities’ GHG emissions inventories, in alignment with the relative national commitments [source]. Therefore, the scenario demonstrates that the momentum of cities as key climate change actors is approaching. In line with the commitment to mitigate climate change, a number of cities worldwide has implemented actions to improve their energy efficiency rates. These actions demonstrated successful outcomes, innovative solutions, and alignment with national policy, which makes the good practices of cities for energy efficiency improvements. The collection developed by the Copenhagen Centre on Energy Efficiency presents these cases within the framework of a methodology inspired by the “Best Policy Practices for Promoting Energy Efficiency” publication by the United Nations Economic Commission for Europe [source].