In this paper, I analyze the ability of monetary policy to stabilize both the macroeconomy and financial markets under two different scenarios: fixed- and variable-rate mortgages. I develop and solve a new Keynesian dynamic stochastic general equilibrium model (DSGE) that features a housing market and a group of constrained individuals who need housing collateral to obtain loans. A given share of constrained households borrows at a variable rate, whereas the rest borrow at a fixed rate. I consider two alternative ways of introducing a macroprudential approach to enhancing financial stability: one in which monetary policy, using the interest rate as an instrument, responds to credit growth; and a second one in which the macroprudential instrument is instead the loan-to-value ratio (LTV). The results show that when rates are variable, a countercyclical LTV rule performs better in stabilizing financial markets than monetary policy. However, when rates are fixed, even though monetary policy is less effective in stabilizing the macroeconomy, it does a good job in promoting financial stability.

This paper introduces imperfect knowledge and learning behavior of economic agents into the Kiyotaki and Moore model and studies the interaction of agents' collateral price beliefs, collateral constraint, and aggregate economic activity over the business cycle. It establishes the E-stability condition and the convergence of the real time learning process. In addition, it shows that learning strengthens the role of collateral constraints in aggregate fluctuations.

We examine a general equilibrium model with collateral constraints and increasing returns to scale in production. The utility function is nonseparable, with no income effect on the consumer's choice of leisure. Unlike this model without a collateral constraint, we find that indeterminacy of equilibria is possible. Hence, business cycles can be driven by self-fulfilling expectations. This is the case for more realistic parameterizations than in previous, similar models without these features.

In this paper I develop a dynamic stochastic general equilibrium model of credit frictions in which the production technology provides a U-shaped average cost curve, enabling endogenous solutions for firm size and quantity. Firms weigh the present value of future net revenues against the opportunity cost of staying in business in their entry or exit decisions. I find that credit frictions increase variable investment costs and result in a larger firm size and a smaller number of firms in the steady state. As the economy deviates from the steady state, however, the presence of credit frictions increases fluctuation in the number of firms, raising market entry during an economic upturn and market exit during a downturn. Also, I find that allowing free entry mitigates some of the effects of credit frictions due to macroeconomic fluctuations. In addition to the homogeneous-firm model, I examine the model when firms have heterogeneous access to credit and find that different credit access gives rise to different firm sizes in the steady state. Firms with easier access to credit become larger than those with less access to credit. Heterogeneous credit access also means that these two types of firms will respond differently to a common technology shock.