Workers will not pay for general on-the-job training if contracts are not enforceable. Firms may if there are mobility frictions. Private information about worker productivities, however, prevents workers who quit receiving their marginal products elsewhere. Their new employers then receive...

Suppliers who are better informed than purchasers, such as physicians treating insured patients, often have discretion over what to provide. This paper shows how, when the purchaser observes what is supplied but can observe neither recipient type nor the actual cost incurred, optimal provision...