Optimal Voting Rules

We derive the incentive compatible and ex-ante welfare maximizing (i.e. utilitarian) mechanism for settings with an arbitrary number of agents and alternatives where the privately informed agents have single-crossing and single-peaked preferences. The optimal outcome can be implemented by modifying a sequential voting scheme that is used in many legislatures and committees. The modification uses a flexible majority threshold for each of several alternatives, and allows us to replicate, via a single sequential procedure, the entire class of anonymous, unanimous, and dominant strategy incentive compatible mechanisms. Our analysis relies on elegant characterizations of this class of mechanisms for single-peaked and single-crossing preferences.