As we saw in the Introduction, climate change is an increasingly important challenge for cities. The quote above, taken from the 2007 Fourth Assessment Report of the IPCC, suggests that this is because climate change will add stress to urban areas that are already under pressure from the effects of, for example, population growth, ill health, urban expansion, inadequate services, decaying infrastructure or persistent poverty. In urban areas, these risks are combined in distinct ways to create particular challenges, as well as opportunities, for living in the city. For others, climate change presents a more fundamental challenge to the organization and operation of socities. Understanding the impact that climate change will have in cities, therefore, means understanding how it will add to, or relieve, existing vulnerability. In its most fundamental terms, vulnerability relates to the exposure of people or places to risk. The extent to which cities may be vulnerable to climate change is, therefore, a product of the risks that they may experience – the impacts associated with different aspects of climate change – the ways in which they are exposed to those risks, and their ability to respond to risk (Box 2.1).