Over the past decade many Western local governments have been experimenting with initiatives inviting the participation of ordinary citizens in public policy-making. However recurrently popular the idea of such participation, its practice is usually quite disappointing. Few ordinary citizens take an interest in participating in policy-affairs, and official policy-makers, anyhow, often seem to lack the will or means to contemplate or adopt their policy-suggestions. Hence, policy participation by ordinary citizens has a strong tendency to “evaporate”. In this article I address the question why this might be so. Drawing from the literature and qualitative interviews, I suggest five broad causal mechanisms to account for the phenomenon of participatory evaporation. This phenomenon seems, in fact, so overdetermined that it is hard to think of the conditions under which policy participation by ordinary citizens might work at all.