The current body of law governing the conduct of police and prosecution during the investigative phase of criminal proceedings encompasses an enormous amount of rules. At the same time, a restrained approach with regard to the judicial supervisory role of investigative propriety is visible in case law while it remains unclear whether and to which extent other institutions have a supervisory role in this respect. This research looks at the current system of supervision on police and prosecutorial conduct in the context of criminal law proceedings from the viewpoint of criminal law standard. After all, creating rules for the conduct of law enforcement entails a certain obligation to ensure rule-compliance. After illustrating the complexity of the current legal framework as well as the complexity of reasons underlying its norms, the study focuses on the supervision of the conduct of police and prosecution. Based on the specific characteristics of the current Dutch criminal procedural law, the study develops a framework for an adequate system of supervision. The study then describes how currently supervision on police and prosecutorial conduct is organised and finally evaluates this in light of the requirements of adequate supervision as set out in previous chapter.