The separation of investment and commercial banking has had a long tradition primarily in the US. Since the global financial crisis similar rules are being discussed by rule-makers all over the world, now however with various modifications. The German legislator has just decided on their introduction. Traditionally, such rules have been justified by considerations with regard to single financial institutions, but since the financial crisis the question of system stability has come to the fore. By no means has it been proven, however, that the separation of investment and commercial banking is able to reduce systemic risks. In addition, such a regime restricts institutional diversity and thus threatens to have destabilizing effects itself. The modifications which are currently being discussed as alternatives to the classical separate banking system cannot dispel these doubts. A restriction of activities based on the US-american Volcker Rule causes substantial problems with respect to identifying prohibited transactions. Moreover, it raises concerns about an increase in unregulated shadow banks. The intra-group separation of business lines which is planned and/or adopted on the European level, in Great Britain and Germany does not offer any promising leverage against systemic risk spreading: According to applicable corporate law, individual corporate affiliates are by no means entirely unconnected, but remain effectively integrated in a corporate group. Moreover, investor confidence in the entire group will be shaken even in case of difficulties of single divisions only. To sum up, the reservations against structural rules introducing a separate banking system are predominant, as such rules massively intervene in grown bank structures, at the same time being very complex, and for this reason posing the risk of circumvention as well as the risk of unintended side-effects. An incentive-based, more focused regulation of securities trading seems to constitute a much better alternative.