In this paper, the discretion of criminal prosecution is understood as a principle which addresses the issue of mandatory character of prosecution for the ex-officio crimes, within the margins of public interest. It is interpreted that the scope of application of the discretion principle is exclusively related to the public prosecutor and the ex-officio crimes, and that its' actual reach is limited by the broadness of the legal concept of the crime. In the course of discussion on criminal policy reasons by which the theory justifies the discretion principle and on the application requirements in comparative legal systems, the author identifies it as a divertive model, based on consensual and restorative justice ideas, whose purpose is rationalization of the criminal procedure and accomplishment of some extra-procedural and political goals. On the grounds of the content analysis of both guiding principles of criminal actions, the author points out their differences and similarities, and concludes that the opportunity principle corrective and complementary to the legality principle, and not only its counterpart. The last part of paper contains critical analysis of the legislatively enumerated cased of the discretionary prosecution in Serbian criminal law.