In Chapter 2, the classification of data processed by MDTs under the General Data Protection Regulation (GDPR) is examined. While the data processed by MDTs is typically linked to the category of biometric data, accurately classifying the data as special category biometric data is complex. As a result, substantial amounts of data lack the special protections afforded by the GDPR. Notably, data processed by text-based MDTs falls entirely outside the realm of special protection unless associated with another protected category. The book advocates for a shift away from focusing on the technological or biophysical parameters that render mental processes datafiable. Instead, it emphasises the need to prioritise the protection of the information itself. To address this, Chapter 2 proposes the inclusion of a new special category of ‘mind data’ within the GDPR. The analysis shows that classifying mind data as a sui generis special category aligns with the rationale and tradition of special category data in data protection law.