Cities face a mounting challenge from climate change. In developed and developing countries alike, rising temperatures, changing rainfall patterns, higher sea levels, and more frequent and severe extreme events such as droughts and floods threaten to overwhelm urban infrastructure, services and management systems. City officials recognise the need to adapt to climate change, and use scientific evidence to support their plans for doing so. But the precise details of these changes and the local impacts they will have cannot be predicted. This briefing explains how decision makers can draw on scientific data while simultaneously managing the uncertainty inherent in future projections, and highlights the forward-looking city officials across the world who are proving themselves to be ‘urban adaptation leaders'.