Climate change poses a massive threat to development. The poorest populations of poor countries – the Least Developed Countries, Small Island Developing States, and the nations of Africa – face the concentrated challenge of tackling the worst of the impacts with the least capacity to do so. Clearly, adaptation to climate impacts must be seamlessly integrated into any development planning and policy. This four-step plan for mainstreaming climate change aims to fulfil that need. A ‘learning by doing’ approach, it focuses first on national capacity to ensure that development in all sectors and at all levels is effectively climate-proofed.