In 2008, following an internal investigation conducted by a law firm, Siemens AG settled ongoing corruption proceedings with the German and American authorities. German legal scholars critisized this approach and questioned its compliance with German law. This thesis identifies the legal basis for this criticism and examines the compliance of internal investigations with public international, corporate, capital markets, competition and data protection law, as well as employees' fundamental rights and the standards imposed on legal professionals. It takes into account the SEC's procedure and the general approach to internal investigations in practice. The analysis is based on research conducted in Germany and the USA as well as on interviews with the attorneys and employees of the SEC and the Munich public procecutor involved in the proceedings in question. The author is now an attorney specializing in litigation and internal investigations in an international law firm.