Today, more than half the world’s population lives in cities—a figure expected to grow by 2.4 billion by 2050. Cities are at the heart of humanity’s future, but they are also ground zero for some of our biggest challenges: climate change, social inequality, and economic fragility. To house the growing urban population and achieve the U.N.’s Sustainable Development Goals (SDGs) while leading the fight against climate change, cities must embrace transformative, sustainable urban development. The rapid expansion of urban areas is no longer just a trend—it’s a crisis.