World population is expected to increase to 9 billion people in just three decades. Two out of three people will probably be living in cities by that time. New cities will have to be created and built, and old cities will have to be adapted to considerably larger populations. This calls for a fundamental understanding of the complex structures and interrelated dynamics of cities, in order to address accelerating global challenges such as climate change, lack of energy and other resources, and environmental degradation. Recent studies show that the complexity of cities can be studied as mathematical and scientific analyses. Some features show remarkable likenesses between cities of different sizes, and may be expressed as “superlinear” equations, showing an exponential growth of social interaction, production, and creativity as cities grow larger. However, these interrelations are often overlooked, leading to less than ideal and sometimes counterproductive plans, policies, and measures. Practical and relevant academic knowledge must be made accessible to practitioners and policymakers through new and open arenas for exchange and capacity building. Research centers and global organizations have a shared responsibility to contribute to better governance for sustainable urban development.