Whistleblowing and whistleblowers have received a great deal of attention over the last decade. By now, we know quite a bit about the whistleblower. Whistleblowing (in particular, internal reporting systems) has received less attention. When it comes to effective whistleblowing, we know least about those factors we can most easily influence. Here, the focus is on one possible part of an internal reporting system: the confidential integrity advisor (CIA). Our main research question is: What is the most effective internal reporting system and what role should the confidential integrity advisor play? The analysis of this research is based on different data sources. First, 25 CIAs from many different types of public organizations were interviewed. Second, a survey was carried out among Dutch civil servants (n = 7543). CIAs can play an important role in an effective reporting system. It is important that they are supported by management, have clear descriptions of their duties and tasks, and receive support from supervisors. To improve the effectiveness of the reporting system, addressing the role of supervisors is a logical place to start.