Adverse selection is an important problem in many markets. Governments respond to it with complex regulations: mandates, community rating, subsidies, risk adjustment, and regulation of contract characteristics. This paper proposes a perfectly competitive model of a market with adverse selection....

In an economy with indivisible goods, a continuum of agents and quasilinear utility, we show that equilibrium exists regardless of the nature of agents' preferences over bundles. This contrasts with results for economies with a finite number of agents, which require restrictions on preferences...

We propose a criterion of approximate incentive compatibility, strategy-proofness in the large (SP-L), and argue that it is a useful second-best to exact strategy-proofness (SP) for market design. Conceptually, SP-L requires that an agent who regards a mechanism's “prices” as exogenous to...

We show that kidney exchange markets suffer from market failures whose remedy could increase transplants by 30%–63%. First, we document that the market is fragmented and inefficient: most transplants are arranged by hospitals instead of national platforms. Second, we propose a model to show...