Adaptation to climate change is now widely recognised as an equally important and complementary response to greenhouse gas (GHG) mitigation in addressing climate change. Adaptation consists of deliberate actions undertaken to reduce the adverse consequences, as well as to harness any beneficial opportunities. A wide range of adaptation measures can be implemented in response to both observed and anticipated climate change. Such measures include altering farming practices and crop varieties, building new water reservoirs, enhancing water use efficiency, changing building codes, investing in air-conditioning, and constructing sea walls. Adaptation measures are undertaken both by public and private actors through policies, investments in infrastructure and technologies, and behavioural change. How much adaptation might cost, and how large its benefits might be, are issues that are increasingly relevant both for on-theground projects, as well as in a global context where trade-offs might need to be considered between the costs of climate policies and the residual damages resulting from climate change.