Public trust lacks a precise, theoretically grounded and empirically tested definition, despite the increasing research interest and widespread use of the term in relation to different health care systems as well as other societal institutions. The mass media as well as the scientific community use the term public trust as if there is a common understanding of its meaning. As this is evidently not the case, this article proposes a broadening of an existing conceptualisation of public trust for use in health care system and policy research drawing on wider scholarship on trust from outside health care. In doing so, it further develops an existing conceptualisation of public trust in the health care system as a basis for discussion. In this conceptualisation, the origin of public trust is understood to be in the public sphere, which is situated between the individual, the health care system, the state and other societal institutions. Public trust in the health care system is influenced not only by the health care system itself, individuals’ experiences of it and its media image but also by discourse in the public sphere about individuals’ experiences and the system as a whole. This conceptual framework now needs empirical validation.