The model is general and appropriate to address several questions. We illustrate that by showing that it can replicate standard business cycle properties and to discuss conventional monetary policy in the context sudden stops, when the domestic banking system is often at the epicenter of the crisis. In Chapter 3, we first note that a number of recent theoretical papers show that margins can affect asset prices. Such results are important, for example, to understand the unconventional polices implemented by the Fed during the great recession of 2007-2010. However, empirical evidence is still scarce. We contribute to fill this gap. We show that an aggregate margin-related factor is able to predict future excess returns of the SP 500 and that stocks with high exposures to the cost of buying on margin pay on average higher returns.