This thesis aims to understand the role of credit frictions in general equilibrium models with incomplete financial markets. First, this work studies the importance of debt constraints for the existence of monetary equilibrium in an economy with symmetric information and where money has only the role of store of value. It also characterizes the uniform impatience assumption, an important requirement to equilibrium existence, in terms of asymptotic properties on intertemporal discount factors. Finally, it shows that, if assets are collateralized in order to protect lenders in the case of default, equilibrium always exists in a two-period incomplete markets model of asymmetric information with nominal assets, independently of the financial-informational structure.