We study optimal interest-rate policy in a New Keynesian model in which the economy can experience financial crises and the probability of a crisis depends on credit conditions. The optimal adjustment to interest rates in response to credit conditions is (very) small in the model calibrated to match the historical relationship between credit conditions, output, inflation, and likelihood of financial crises. Given the imprecise estimates of key parameters, we also study optimal policy under parameter uncertainty. We find that Bayesian and robust central banks will respond more aggressively to financial instability when the probability and severity of financial crises are uncertain. JEL Classification: E43, E52, E58, G01

This paper examines how the presence of uncertainty alters allocations and prices when the nominal interest rate is constrained by the zero lower bound. I conduct the analysis using a standard New Keynesian model in which the nominal interest rate is determined according to a truncated Taylor rule. I find that an increase in the variance of shocks to the discount factor process reduces consumption, inflation, and output by a substantially larger amount when the zero lower bound is binding than when it is not. Due to the zero lower bound constraint, policy functions for the real interest rates and the marginal costs of production are highly convex and concave, respectively.As a result, a mean-preserving spread in the shock distribution increases the expectation of future real interest rates and decreases the expectation of future real marginal costs, which lead forwardlooking households and firms to reduce consumption and set lower prices today. The more flexible prices are, the larger the effects of uncertainty are at the zero lower bound. JEL: E32, E52, E61, E62, E63

This paper studies optimal government spending and monetary policy when the nominal interest rate is subject to the zero lower bound constraint in a stochastic New Keynesian economy. I find that the government chooses to increase its spending when at the zero lower bound by a substantially larger amount in the stochastic environment than it would in the deterministic environment. The presence of uncertainty creates a unique time-consistency problem if the steady-state is inefficient. Although access to government spending policy increases welfare in the face of a large deflationary shock, it decreases welfare during normal times as the government reduces the nominal interest rate less aggressively before reaching the zero lower bound.