By 2050, two-thirds of the world’s population is projected to live in urban areas, which are major contributors to greenhouse gas emissions. However, according to nuclear engineering professor Daniel Kammen and postdoctoral fellow Deborah Sunter (M.S.’08, Ph.D.’13 ME), cities have great potential to become building blocks of sustainability. In their review in Science, the authors examined the use of renewable energy in urban areas to promote low-carbon, livable cities. They found that cities could transform from being resource drains to becoming “green generators” through advances in smart monitoring and management systems, and through the integration of energy efficiency, renewable power generation and storage and waste management into the urban fabric. They determined that a significant shift away from using personal vehicles would contribute dramatically to cleaner cities. Urban areas also need to develop environmental justice programs as part of the sustainable resource management process. By making more eco-friendly options accessible, particularly to low-income populations, cities can become more livable for all residents.