As health care applications derived from human genetics research are likely to move increasingly from ‘clinic to community’, there is growing interest not just in how patients understand and take up health-related genetic information but also in the views of the wider population, as well as a range of professional groups. In this paper, issues relating public knowledge and public trust are raised and discussed in an attempt to move forward debates about public involvement in genomic research and the role of sociologists within interdisciplinary teams. As the field of public understanding of science has developed, we have seen a shift from a focus on the lack of scientific literacy as problem to a recognition of the range of different knowledges that people have and use as they confront science and technology in their everyday lives. As a mood for dialogue pervades many institutions in their relations with ‘publics’, attention must now be paid to the way in which knowledge and expertise is expressed, heard and acted upon in dialogic encounters. There is increasing concern about public trust in science and calls to increase public confidence, particularly through more open engagement with a range of publics. However, lack of trust or loss of confidence may be constructed as problems rather than reflecting empirical reality, where more complex relationships and attitudes prevail. Lack of trust is often privatized, deeply rooted in lived experience and routinely managed. Trust relations are generally characterized by ambivalence, uncertainty and risk, and are always provisional. Drawing on selected literature and empirical research to review and illustrate this field, this paper argues that scepticism or ambivalence on the part of publics are not necessarily problems to be overcome in the interest of scientific progress, but rather should be mobilized to enhance open and public debates about the nature and direction of genomics research, medicine, and the related social and ethical issues. Just as there can be no resolute expression of public knowledge or public opinion, it is unlikely that there is a resolute expression of public trust in genomics. However, ambivalence and scepticism can be harnessed as powerful resource for change, whether through the mobilization of public knowledges or the development of greater reflexivity within scientific institutions. This demands a sharing of power and greater public involvement in the early stages of policy formation and scientific and medical agenda setting.