Financial factors are central to the recent economic crisis. Most macroeconomic models treat banks and financial intermediation as a veil. These models are unable to account for the recent financial crisis and they cannot be used for policy evaluation. Financial frictions include default on mortgages, disruptions in financial intermediation, and informational asymmetries, among others. In my dissertation, I propose to analyze the effects of policy in economic models characterized by financial frictions. The thesis is composed of three chapters. The first chapter is joint work with Luisa Lambertini and Pinar Uysal. We explicitly model the housing sector, mortgages, and endogenous default as well as nominal and real rigidities in a dynamic stochastic general equilibrium (DSGE) setting. We use U.S. data for the period 1981-2006 to estimate our model using Bayesian techniques. Our starting point is to have an empirically plausible model with endogenous default in mortgages that can explain the main features of the macroeconomic time series. We analyze how an increase in the mortgage default rate can spread to the rest of the economy and result in a recession. Next we examine different policy options that might mitigate the effects of an increase in the mortgage default rate. In the second chapter I develop a two-country DSGE model with global banks (financial intermediaries in one country lend to banks in the other country). Banks are financially constrained on how much they can borrow from households. The main goal is to obtain a framework that captures the international transmission of a financial crisis through the balance sheet of the global banks as well as to explain the insurance mechanism of the international asset market. A negative shock to the value of the capital in one country generates a global financial crisis through the international interbank market. The third chapter uses the above model to analyze the policy challenges that global banks face. In this chapter, I look at how different unconventional unilateral credit policies help to mitigate the effects of a financial disruption. First, the policies are carried out only by the policy maker of the country directly hit by the shock. Consumers of the country where the intervention and the shock take place are better off with policy than without it; consumers from the other country are worse off. Second, I allow for both policy makers to intervene. Both countries intervening help to reduce the negative effects of the country that is not directly hit by the shock but the intervention is not a Pareto improvement.