Disability insurance provides protection against health shocks that limit the ability to work. In most countries, these programmes are large and growing, both in expenditure and in number of recipients. We discuss the traditional trade-off between insurance and incentives in providing this insurance, with a focus on the US and UK experiences. There is substantial evidence on the extent of the labour supply incentive costs of disability insurance, but there has been a lack of evidence on the insurance value until very recently. Further, evidence on errors in the disability insurance process suggests false rejections of genuine claimants is a substantial problem, and these are more serious than false acceptances of healthy applicants. We provide a life-cycle framework for understanding the trade-offs and to evaluate the welfare implications of policy reforms. We argue that reforms should be focused on reducing false rejections and supporting labour market attachment. The difficulty in considering reform is that the design of disability insurance has many aspects that interact and impact on outcomes.