Cost–benefit analysis (CBA) is a process that involves weighing expected project costs against the expected benefits in order to choose the most cost-effective option. It is increasingly being used in the world of disaster risk reduction, both to design programmes and to demonstrate impact, but it has some limitations as an approach, and it is not always the best choice for these purposes. Through a series of case studies, this report emphasises the benefits of CBA while highlighting the need to use it appropriately, and the risk of practitioners who are insufficiently skilled producing results that appear robust but are actually invalid. CBA can be an appropriate option, but always within a wider emphasis on project planning and monitoring. Published in 2010.