For companies it is crucial to keep sensitive information secret. While employees, CEOs and the management board are explicitly obliged to observe secrecy by German Law, these specific duties are missing for shareholders. A general shareholder's duty to observe secrecy can only be derived from the shareholder's duty of good faith. The thesis gives shape to this obligation to confidentiality of shareholders across all personal structured companies and is aimed to develop a gradual structured secret protection concept by means of different levels of confidentiality. The paper especially focuses on possible limits of the obligation to confidentiality. These limits can result from constitutional law, from the fiduciary duty itself, from a possible non-disclosure agreement with the recipient of the information or from a shareholders' resolution with the appropriate majority requirement.