Cities are the world’s future. Today, more than half of the global population—3.7 billion people—are urban dwellers, and that number is expected to double by 2050. There is no question that cities are growing; the only debate is over how they will grow. Will we invest in the physical and social infrastructure necessary for livable, equitable, and sustainable cities? In the latest edition of State of the World, the flagship publication of the Worldwatch Institute, experts from around the globe examine the core principles of sustainable urbanism and profile cities that are putting them into practice.State of the World first puts our current moment in context, tracing cities in the arc of human history. It also examines the basic structural elements of every city: materials and fuels; people and economics; and biodiversity. In part two, professionals working on some of the world’s most inventive urban sustainability projects share their first-hand experience. Success stories come from places as diverse as Ahmedabad, India; Freiburg, Germany; and Shanghai, China. In many cases, local people are acting to improve their cities, even when national efforts are stalled. Parts three and four examine cross-cutting issues that affect the success of all cities. Topics range from the nitty-gritty of handling waste and developing public transportation to civic participation and navigating dysfunctional government. Throughout, readers discover the most pressing challenges facing communities and the most promising solutions currently being developed. The result is a snapshot of cities today and a vision for global urban sustainability tomorrow.