Half of humanity – 3.5 billion people – currently live in cities and by 2055 an estimated 75% of the world's population will live in urban areas. Cities occupy just 2% of the Earth's land, but account for over 70% of both energy consumption and carbon emissions. However, cities present the world's population with the best chance of reducing our ecological footprint. Urban areas are uniquely positioned to lead the greening of the global economy through improvements in transport, energy, buildings, technology, water and waste systems, as well as producing a wide range of economic and social benefits. To achieve this, existing and new-build cities will have to adopt sustainable development strategies, including efficiency gains, innovative infrastructures and technological advancements in order to meet the demands of this rapidly growing urban population. Against this backdrop Climate Action, the UNEP supported communications platform for global business sustainability, is launching Sustainable Cities, an annual publication produced in partnership with the leading organisations within the sustainable urban development sector.