Think tanks and research centres worldwide are devoting in-creasing attention to the growing role of global cities. Why do global cities matter? And why should a think tank dealing with international affairs such as ISPI look at the evolving role of global cities? The obvious answer is: because cities do matter. Urban settings cover barely 2% of the Earth’s surface, yet they host over half of the global population. In the coming decades, the number of mega-cities in Asia and Africa will grow dramat-ically, and this represents a huge challenge in terms of social and environmental sustainability. As urbanisation increases at a steady pace, cities are where most of the world’s GDP, green-house gas (GHG) emissions, and waste are produced. Globalcities, metropolises acting as key hubs in global economic and political networks, matter even more.