Due to the growing complexity of products in financial markets, market participants rely more and more on quantitative models for trading and risk management decisions. This introduces a fairly new type of risk, namely, model risk. In the first part of this thesis we investigate the quantitative influence of model risk on risk management with a main focus on regulation issues. We present frameworks for measuring model risk and backtesting procedures for evaluating model quality. Furthermore, we apply these frameworks to derivatives portfolios. The second part of the thesis concerns interest rate derivatives pricing models. We compare Libor market and discrete string models and find them observationally equivalent. Furthermore, we investigat...