Abstract: Through the creation of the Financial Stability Board (FSB), G20 members have committed to regulate the financial sector across the globe in order to enhance the resilience of the system. Two important points in this agenda are the regulation of OTC derivatives, such as Credit Default Swaps (CDS) and the regulation of Systemically Important Financial Institutions (SIFIs). The first two chapters of this thesis relate to the first point. These papers study the effects of the use of CDS at banks on banks' behavior and stability. The last chapter of the thesis addresses the second point. This chapter discusses the proper assessment of systemic risk, and the characteristics and performance of systemically important banks based on this assessment.