By many estimates, the world has just crossed the point where more than half the world’s population is urban, a trend driven by rapid urbanization in developing countries. Urban centers offer economies of scale in terms of productive enterprise and public investment. Cities are social melting pots, centers of innovation and drivers of social change. However, cities are also marked by social differentiation, poverty, conflict and environmental degradation. These are all issues that not only matter to cities but also lie at the heart of development. As such the time is right to consider afresh the relationship between cities and development. This paper introduces a significant new collection of multidisciplinary papers focused on urbanization and its implications for development. It raises four questions: (i) What is so special about the urban context? (ii) Why is urbanization and urban growth important to development at the present conjuncture? (iii) What are the strengths and limitations of our current state of knowledge about urbanization and development from the policy perspective and finally, (iv) how can a multidisciplinary perspective on the urban context add value to development research and policy?