With the advent of international criminal Tribunals, the role of the prosecution before these Tribunals becomes ever important. Most of the contemporary criminal Tribunals, as will be assessed in this article, endow wide discretionary powers to the prosecution with respect of the commencement of investigation and prosecution. This article will assess the scope of these discretionary powers within the systems of ICTY/ICTR, ICC and in particular the Special Court of Sierra Leone, as the first international mixed Tribunal. Based upon an analysis of the Statutes of these Courts and its available case law, the judicial boundaries of the discretionary powers are surveyed. In doing so, this essay looks into judicial mechanisms in order to monitor and supervise the application of these discretionary prosecutorial powers within the limits of the Rule of Law and the principle of equity. To that end, recent case law of the Special Court of Sierra Leone is invoked in order to secure these limits and to endorse legitimacy. After all, application of prosecutorial powers contrary to the principle of equity, may endanger the legitimacy of the work of international criminal Tribunals. Therefore, the author concludes with several proposals to improve the transparency of the prosecutorial decisions with respect to the commencement of investigations before international criminal Tribunals.