Outline of the Symposium: Present discussions on the implications of the General Data Protection Regulation (GDPR) for medical practice and health research mostly target the passive collection of health data. This workshop proposal shifts the lens of analysis to the scarcely researched and rather different phenomenon of the active sharing of health data within the framework of Citizen Science projects. Starting from this focus, we will query whether data processing requirements under the GDPR impacts the advancement of Citizen Science for health research. A number of tensions between the two aims will be identified both in abstract terms and ‘in practice’ by analysing three Citizen Science scenarios and drawing parallels with the experience of ‘collective’ Clinical Trials. The limited studies and literature on the topic makes this workshop an exploratory reflection on key tensions, with the aim of opening the way for further research. This discussion is inspired by the need to guarantee that opportunities of Citizen Science for health research will not be unduly curtailed by the advent of the GDPR but also to ensure that Citizen Science is implemented in ways that are consistent with the GDPR.