Ageing of hazardous installations has been the subject of increasing attention in the past decade, both by public authorities and industry. Indeed, worldwide, and in particular across OECD countries, many of the currently operating chemical facilities have reached or exceeded the end of their nominal design life which is typically set at 20 to 25 years. Many of these facilities were built in the post Second World War period and in 2016 facilities can now be up to 75 years old and still in service. This raises questions as to how best to manage these older facilities, and how to anticipate ageing in newer ones. In 2013, the OECD Working Group on Chemical Accidents initiated a project on Ageing of Hazardous Installations, the objective of which was to get a better understanding of what ageing is and its implications. The project sought to identify the risk factors associated with ageing facilities, establish whether ageing is a cause of accidents, and discover how ageing is being approached by public authorities and whether ageing is addressed as a specific subject in policy and regulations. The results of the activities conducted within the framework of this project are presented in this report.