Collateralized Debt Obligations (CDOs) are the most prominent example of portfol- related credit derivatives. They make it possible to diversify and transfer credit risk by pooling and redistributing the risks of an underlying portfolio of defaultable assets. It comes as no surprise that the dependence structure of portfolio assets is crucial for the valuation of CDO tranches. The standard market model is the Gaussian copula model, which uses only one parameter to summarize the correlations of default times in the underlying credit portfolio. Comparable with the volatility smile from option...