Abstract: With respect to climate change, the principal focus of both research and public policy has been on mitigation – on reducing greenhouse gas emissions so as to reduce anticipated adverse effects. But it is increasingly clear that adaptation must also be a high priority. Climate-related risks – including flooding, extreme heat, wildfires, droughts, and hurricanes – are quite serious and are likely to grow over time. Creative and not-so-creative measures to nudge, incentivize, and mandate adaptation may well have benefits far in excess of costs – and may, in fact, deliver higher net benefits than some efforts at mitigation. Because significant climate change is now occurring, and will almost certainly create increasing risks over time, adaptation is essential. It must be carefully assessed with attention to (a) its aggregate effects on social welfare and (b) its distributional impacts. Cost-benefit analysis can much help with (a), but it can run into serious concerns, not only because of (b), but also because of epistemic gaps and because of its failure, in some cases, adequately to capture welfare effects.