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. Check out an excerpt of the book below.