This paper studies financial intermediation in a general equilibrium overlapping generations model. Indivisible investment projects combine with informational imperfections to create a (hidden action) moral hazard problem and introduce a role for third-party monitoring. Agency costs at the intermediary level are also considered. Under some conditions, monitors can be viewed as banks facing a non-trivial portfolio diversification problem. Equilibria are derived in which a large nationwide bank coexists with a number of community-regional banks, a structure of strong empirical relevance. Policies such as a mandatory reserve requirement are shown to have substantial effects on the levels of investment in the economy.

We study ex post efficient policy responses to a run on the banking system and the ex ante incentives these responses create. We show that the efficient response to a run is typically not to freeze all remaining deposits, since doing so imposes heavy costs on some individuals. Instead, once a run is underway, (benevolent) government institutions would allow additional deposit withdrawals, placing further strain on the banking system. When depositors anticipate these extra withdrawals, their incentive to participate in the run increases. In fact, ex post efficient interventions can generate the conditions necessary for a self-fulfilling run to occur.