Science museums perform representations of science and that of its publics. They have been called to intervene in nanotechnology within global public policy programs expected to develop the field. This paper discusses the case of European science museums. It starts by examining the case of a European project that involved science museums working on nanotechnology. This example illustrates a "democratic imperative" that European science museums face, and which implies a transformation of their public role. It offers a path for the analysis of the current evolution of European science communication perspective – from "public understanding of science" to "scientific understanding of the public" – and of the political construction this evolution enacts.