Is it permissible for the state to censor or suppress conspiracy theories, even within liberal democracies? According to a number of political and legal theorists, it is. In this paper, I will argue that the state may sometimes censor conspiracy theories, but it should be permitted to do so only after very strict conditions have been met. I shall first offer some brief thoughts about the definition of ‘conspiracy theory’. I will then critique one existing attempt to address this issue (...) – namely Cíbik and Hardoš’s public reason approach. Next, I shall outline my own proposal. I will argue that we should sometimes consider conspiracy theorising to be a form of discriminatory speech against vulnerable individuals and groups, and we can consider it to be a form of defamation in these cases. Consequently, the state may sometimes be permitted to enact civil laws to sanction such theorising. Finally, I will outline some of the conditions that should be met before state censorship can be considered. (shrink)