Political scientists should not expect a direct causal impact on the actions of politicians and policy makers. They are more likely to influence the climate of ideas, which in turn can shape public policy. In general, politicians and policy makers are hungry for ideas and want to see themselves at the forefront of new debates. In particular, they are interested in findings that they and their advisers cannot create for themselves. The techniques of advanced political science and debates within it are far from being arcane for they offer a new approach and provide robust evidence about politics and policy. Political scientists should not aim to be like journalists, commentators or advisers as they will usually perform less well than these talented practitioners. By communicating in conferences, tweeting, blogging and public speaking they will find that politicians and civil servants will come looking for them as well as the other way round. The article reviews studies of the diffusion of ideas and the ways in which ideas influence politicians and other policy makers, which back up an indirect approach to impact.