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. By highlighting the best practices from cities around the world, the authors examine the policies and technologies by which cities can bring about a renewable energy future. It provides concrete examples of how municipal leaders and administrators can accelerate the switch to renewable energy at the local level by acting as planners, regulators, financiers and operators of urban infrastructure.