Until now, there has been no theoretical foundation that explains why organizations implement whistleblowing systems. By understanding whistle-blowing systems as an instrument that is desired by society, the legitimacy theory could be transferred to the whistle-blowing concept. A survey of German managers shows that legitimacy theory may be supported. Further insights into legitimacy theory are given by the motivation for the design of the implemented systems. The survey shows that, in particular, the implementation of external whistle-blowing systems is seemingly not driven by desired effectiveness. This supports legitimacy theory, since it reveals that external systems are symbolic rather than substantive systems. [---]