More than half of the global population live in cities, which are major concentrations of vulnerability to climate change. Cities are also major emitters of greenhouse gasses. Consequently they are key to mitigating global climate change and reducing the impacts of climate change on people and infrastructure. This role is being increasingly recognised through the policy and planning measures of individual cities and their collective action in the global climate debate. This paper reviews the potential impacts of climate change on cities and the challenges faced by city planners to manage these risks. An integrated assessment system for analysing climate change in cities is being developed by the Tyndall Centre for Climate Change Research. The principles of this system are introduced before identifying remaining research questions.