In a common agency game, several principals try to in°uence the behavior of an agent. Common agency games typically have multiple equilibria. One class of equilibria, called truthful, has been identi¯ed by Bernheim and Whinston and has found widespread use in the political economy literature....

We consider a pure exchange economy, where for each good several trading institutions are available, only one of which is market-clearing. The other feasible trading institutions lead to rationing. To learn on which trading institutions to coordinate, traders follow behavioral rules of thumb...

We study competition among market designers who create new trading platforms, when boundedly rational traders learn to select among them. We ask whether ‘Walrasian’ platforms, leading to market-clearing trading outcomes, will dominate the market in the long run. If several market designers...