Under the European Union’s General Data Protection Regulation, companies will be required to completely erase the personal data of any citizen who requests that they do so. For businesses that use blockchain, specifically applications with publicly available data trails such as Bitcoin and Ethereum, truly purging that information could be impossible. “Some blockchains, as currently designed, are incompatible with the GDPR,” says Michèle Finck, a lecturer in EU law at the University of Oxford. EU regulators, she says, will need to decide whether the technology must be barred from the region or reconfigure the new rules to permit an uneasy coexistence.