Abstract Background Health data-sharing initiatives are central to European and national e-health strategies, aiming to improve healthcare quality, inform policymaking, and drive research. Public trust is crucial for their success, influencing public participation and policymakers’ legitimacy. This study investigates the role of public trust in the health policy process at both the European level and in Italy, France, and Switzerland to determine 1) if a common conceptual understanding of public trust across different countries and policy stages exists, and 2) if policymakers explicitly discuss and implement trust-building measures in their legislative work Methods A total of 60 interviews were conducted with 16 European, 15 Italian, 14 French, and 15 Swiss policymakers from the World Health Organization, the Council, Parliament, and Commission at the European level, along with representatives from the Ministry of Health, Parliament, regional councils, local health authorities, frontline staff, and relevant agencies at the national levels Results Preliminary results reveal that a common definition of public trust in health data sharing is missing. Associations to public trust are observed at the European level with citizens’ reassurance about their sensitive data being shared, and in Switzerland with data security. In France, public trust is connected to public engagement, while no distinct patterns were identified in Italy. Findings also reveal a consensus among interviewees on the central role public trust plays in health data-sharing initiatives; yet public trust is perceived as a vague concept, often addressed implicitly without a clear strategy Conclusions The study reveals widespread ambiguity among policymakers regarding the definition of public trust and its translation into policy. Practical guidance is crucial to effectively integrate elements of public trust into policymaking, thereby actively reinforcing trust in health data sharing through legislative efforts Key messages • While policymakers recognize the importance of public trust for data-driven health initiatives, they lack a common conceptual understanding on what trust is and how to build it. • Guidance is needed to help policymakers actively contributing building trust in health data sharing through their legislative work.