Trust is believed to be particularly salient to the provision of health care, and since the establishment of the National Health Service (NHS) in the UK, trust has played an important role in the relationships between its three key actors: the state, healthcare practitioners, and patients and the public. Service users trusted the judgement, knowledge and expertise of health professionals to provide a competent service that met their needs, and they trusted the state to ensure equity in the allocation of public goods and services. These implicit or taken-for-granted trust relationships have, it is claimed, been challenged as a result of the introduction of changes in the organisation and funding for the health service, in the regulation and performance assessment of health professionals, and in public attitudes to health care and scientific medicine. This paper considers the influences of social changes and recent policy and professional initiatives in health care on the structure of trust relations in health care in the UK. It presents a theoretical framework for examining trust relations using the NHS as a case study and concludes with an agenda for future research.