The EU’s General Data Protection Regulation (GDPR) takes effect on May 25, 2018. It will require all businesses that process EU citizens’ personal data to take lots of measures to protect their privacy. The GDPR also provides EU citizens with a right to erasure: to be able to require that businesses holding their data irrevocably erase the data upon request (also known as the “right to be forgotten”). This right is not absolute and has many exceptions (archiving in the public interest, public health purposes, etc.). But this may end up putting the GDPR on a collision course with blockchain technologies in unexpected ways.