Before 2007, the European financial system benefited from a flourishing economy. Nobody would have assumed that only a few years later the situation would look entirely different. At the time, the discussion of contagion effects, in particular within financial groups looked out of kilter. Financial groups were predominantly seen as strong symbol of strength due to the mutual support of affiliates and efficiency gains as a result of the potential considerable diversification across entities. Contagion across entities or other adverse effects were mostly ignored or downplayed. This book tries to assess potential adverse effects within and across groups while acknowledging the benefits of a group structure, such as diversification and potential synergy effects.