Under the GDPR, Supervisory Authorities (SAs) have a duty to cooperate in order to ensure consistent application of the Regulation. In cases that have a cross-border component, the SAs of the European Economic Area (EEA), i.e. the 28 EU Member States (27 as of 31 January 2020) plus Iceland, Norway and Liechtenstein, have a range of tools at their disposal to facilitate harmonisation. These are: • mutual assistance;• joint operation;• the One-Stop-Shop cooperation mechanism.