Aim/Purpose: The present work focuses on French PhD students’ well-being: an understudied working population thus far, which impedes the development of evidence-based policies on this issue in France.The focus of this work is the well-being of French PhD students, on which almost nothing has been published thus far, impeding any evidence-based policy on this issue to be carried out in France. Background: Research studies from several countries have shown that carrying out a PhD can be a difficult experience resulting in high attrition rates with significant financial and human costs. Methodology: The two studies presented in this article focus on biology PhD students from University Lyon 1, a very large French university (~40,000 students). A first study aimed at measuring the mental health and well-being of PhD students using generalist and PhD-specific tools. In a second study, we carried out and assessed a positive psychology intervention (PPI) aimed at improving PhD students’ well-being. Contribution: Our work is one of the first characterizations of French PhD students’ mental health and well-being. As with other recent studies conducted in Western coun-tries, we found a high level of mental distress among PhD students. Our work also underlines the importance of taking many dimensions of the PhD (not only supervisor behaviour) in order to understand PhD student well-being. Cultural specificities are highlighted and can help inform the design of interventions adapted to each situation. The PPI showed pre-to-post positive changes on PhD students’ well-being. Further research is needed on a larger sample size in order to detect more subtle effects. However, these results are promising in terms of interventions that help reduce PhD student distress. Findings: Study 1 involved 136 participants and showed that a large fraction of the PhD students experiences abnormal levels of stress, depression, and anxiety. We found that career training and prospects, research experience, and the impact of carrying out a thesis on health and private life have more impact on PhD students’ mental health than the supervisors’ behaviour. French PhD students’ well-being is specifically affected by career uncertainty, perceived lack of progress in the PhD, and perceived lack of competence compared to UK PhD students well-being, which suggests cultural differences about the PhD experi-ence in France compared to other countries. In study 2, the scores of the test and control groups (N = 10 and N = 13, respectively) showed a clear effect of the intervention on reducing anxiety. Impact on Society: The high levels of mental health issues and reduced well-being in French PhD students reported in this study underline the importance of developing interventions in this field. Improving the supervisor-student relationship is one possibility but is not the only one. Interventions aimed at learning how to cope with the research experience and with the uncertainty with career pathways, and a good balance between PhD work and personal life present other promising possibilities