One of the central aims of James Buchanan’s long and fruitful career was to identify constitutional rules that could contain rent seeking. A central task for constitutional theorists is to identify constitutional rules that prohibit or limit rent seeking, in order to ensure that a society’s economic system benefits all and preserves their liberty. However, there is a related, but equally dangerous phenomenon that Buchanan does not explicitly address as a variant of rent seeking: the attempt by sectarian groups to capture governmental apparatus to impose their values on others. The goal of these ideologues is not economic gain, but evaluative gain. Co-opting state power, they force those with different values to share or at least submit to their own sectarian vision of the good society. Like rent seeking, this activity tends to undermine the gains from trade in a market order. These activities give the sectarian an unequal gain in utility and may impose a utility loss on others. In this broad sense, sectarian ideologues collect a rent. If we can specify the sense in which ideologues collect a rent, we can expand the reach of Buchanan’s research program. Towards this end, I develop an account of what I shall call ideological rent seeking and the ideological rent seeker. I then extend Buchanan’s approach to constitutional choice to cover the mitigation of ideological rents. The best constitutional rules are those that constrain a weighted sum of economic and ideological rent seeking.