»Activist Shareholders.Guiding Principles on the Role of the Shareholder, Legal Restrictions of Shareholder Activism and Opportunities to Respond«: The author examines the permissibility of shareholder activism regarding corporate and capital market law based on the guiding principles of the role of the shareholder within the German stock corporation. The thesis further provides an overview of company's response options and examines the legal admissibility of defensive measures. The author concludes that the current legal situation regarding shareholder activism is sufficient but minor legal amendments would be useful.