Financial crises are widely argued to be due to herd behavior. Yet recently developed models of herd behavior have been subjected to two critiques which seem to make them inapplicable to financial crises. Herds disappear from these models if two of their unappealing assumptions are modified: if...

In recent financial crises and in recent theoretical studies of them, abrupt declines in capital inflows, or sudden stops, have been linked with large drops in output. Do sudden stops cause output drops? No, according to a standard equilibrium model in which sudden stops are generated by an...

Banks and financial intermediaries that originate loans often sell some of these loans or securitize them in secondary loan markets and hold on to others. New issuances in such secondary markets collapse abruptly on occasion, typically when collateral values used to secure the underlying loans...

In standard approaches to monetary policy, interest rate rules often lead to indeterminacy. Sophisticated policies, which depend on the history of private actions and can differ on and off the equilibrium path, can eliminate indeterminacy and uniquely implement any desired competitive...

The optimal choice of a monetary policy instrument depends on how tight and transparent the available instruments are and on whether policymakers can commit to future policies. Tightness is always desirable; transparency is only if policymakers cannot commit. Interest rates, which can be made...

We argue that discretionary monetary policy exposes the economy to welfare-decreasing instability. It does so by creating the potential for private expectations about the response of monetary policy to exogenous shocks to be self-fulfilling. Among the many equilibria that are possible, some have...

We analyze the setting of monetary and nonmonetary policies in monetary unions. We show that in these unions a time inconsistency problem in monetary policy leads to a novel type of free- rider problem in the setting of nonmonetary policies, such as labor market policy, fiscal policy, and bank...

We analyze two monetary economies - a cash-credit good model and a limited participation model. In our models, monetary policy is made by a benevolent policymaker who cannot commit to future policies. We define and analyze Markov equilibrium in these economies. We show that there is no time...

Why is it that inflation is persistently high in some periods and persistently low in other periods? We argue that lack of commitment in monetary policy may bear a large part of the blame. We show that, in a standard equilibrium model, absence of commitment leads to multiple equilibria, or...

We provide an introduction to optimal fiscal and monetary policy using the primal approach to optimal taxation. We use this approach to address how fiscal and monetary policy should be set over the long run and over the business cycle. We find four substantive lessons for policymaking: Capital...