I begin by examining some largely false leads from the Greeks in defining the nature of scientific citizenship in a democracy. Nevertheless, the lineage from Plato to positivism does provide a context for understanding the evolution of the modern conception of expertise and the distinct problems it poses to modern democracies. These problems revolve around issues of institutionalisation —specifically, how to design institutions that respect the idea of knowledge as a principle of social order without succumbing to rule by expertise—. After analysing two recent German proposals along these lines, I defend the institutionalisation of «consensus conferences», or citizen juries. Finally, I consider some the more general social epistemological implications of the role of «citizen scientist ».