This report assesses the flexibility potential of data centres and analyses challenges and opportunities for using that potential. The report looks at different flexibility needs: market-serving flexibility to balance supply and demand; grid-serving flexibility to manage power system bottleneck; and system-serving flexibility to maintain power system stability. It assesses strategies available to data centres: enabling workload flexibility; utilising supporting infrastructure; and integration of additional flexibility assets. The report indicates that useful potentials of data centre flexibility exist, but that the deployment of data centre flexibility is limited by operational and economic barriers, which vary across different data centre types. A suit of policy options is suggested covering market design, options within sustainable product policy; and the link between renewable procurement and flexibility.