Urban areas are now home to more than half the population of OECD countries. Megacities like Tokyo with more than 35 million people and Mexico with about 18.5 million, and large agglomerations such as Montreal, Helsinki, Madrid and Stockholm are often called "engines of national growth." They represent an important part of the national economy (up to 50% for Budapest, Seoul and Helsinki) and feature higher GDP per capita and productivity levels than their countries' averages. But the urban paradox is that cities also harbor large pockets of unemployment and poverty and suffer from ills such as congestion, pollution and crime. So are urban regions sustainable in the long term? Balancing the economic advantages of cities with their accompanying problems, policymakers are rethinking the strategies to keep these "engines" running smoothly. This book is a synthesis report drawing from OECD metropolitan reviews. Based on an international database of 78 metro-regions, it provides indications related to large cities' performance within their countries. The report also addresses key dilemmas, including competitiveness and social cohesion, intergovernmental relationships and urban finance.--Publisher abstract