This report aims to help those responsible for the safety of reservoirs. These include engineers appointed under current legislation, personnel who visit reservoirs in the course of their duties, staff who operate and monitor reservoirs, and enforcement authority engineers. The scope of the report is limited to water-retaining structures: some types of waste impoundments, such as tailings dams, may suffer similar types of malfunction, but these are not included. Although the focus of the report is on incidents at dams in Great Britain, reference is made to a few international incidents. International experience is particularly helpful for those types of dam that are not commonly found in Great Britain. The report begins with an introduction in Section 1. The background to the subject is briefly outlined, the value of the national incident database is demonstrated and the need for post-incident reporting and investigation is emphasised.