This report explores potential for urban communities to scale-up renewables by 2030, based on estimated energy use in 3,649 cities around the world. The authors find that every city has massive potential to cost-effectively boost renewable energy use at the local level. They outline three priority areas where cities can take action: renewable energy in buildings (for heating, cooling, cooking, and appliances), sustainable options for transport (electric mobility and biofuels) and the creation of integrated urban energy systems.