Abstract
In mechanism design, strategy-proofness is often said to be desirable because it makes it easy for agents to decide what to do. However, some strategy-proof mechanisms are easier to understand than others. To address this problem, I propose a new solution concept: Obviously Strategy-Proof (OSP). Using a formal cognitive model, I show that a mechanism is OSP if each agent's dominant strategy can be verified without contingent reasoning. I show that a choice rule is OSP-implementable if it can be carried out by a social planner under a particular regime of partial commitment. Finally, I characterize the set of OSP mechanisms in a canonical setting, for that encompasses private-value auctions with unit demand and binary public good problems.