The present two tier system in the German corporation has been developed by the one tier system. The supervisory board was not only a monitoring instrument, but also responsible for the management. The shareholders demanded an external audit because the internal audit by the supervisory board was not objective. Insofar, the external auditors fulfil a "gatekeeper" function for the shareholders and an "assistant" function for the supervisory board. The convergence and competition of the one- and two tier system has mainly influenced the reform process from the "code de commerce" to the "accounting law modernization act".