Introduction This tool addresses the challenges of prosecuting perpetrators of crimes such as genocide, crimes against humanity and war crimes. Prosecutions form one of the central elements of an integrated transitional justice strategy, aimed at moving a society beyond impunity and a legacy of human rights abuse. While this publication seeks to draw lessons from past experiences, there is an obvious limitation: impunity has been the norm for serious violations of national and international law, while successful prosecutions are the exception. Nevertheless, there have been significant advances over the past two decades. This tool presumes that long-term and sustainable solutions to impunity should aim mostly at building domestic capacity to try these crimes.1 The Secretary-General’s report, “The rule of law and transitional justice in conflict and post-conflict societies,” states that “[of] course, domestic justice systems should be the first resort in pursuit of accountability.”2 This basic presumption is not affected by the establishment of the International Criminal Court, since the Court will assume jurisdiction only where States are “unwilling or unable genuinely” to investigate or prosecute themselves.3 Moreover, the Court will have jurisdiction only where States are parties to the Rome Statute or in situations referred to it either by a State itself or by the United Nations Security Council, and then only over crimes committed after July 2002. The focus of this tool is therefore mainly on the strategic and technical challenges that these prosecutions face domestically.4 Devising a well-grounded strategy and building adequate technical capacity will serve to bolster the independence and impartiality of prosecutorial initiatives. In some situations, however, it will not be possible to act through the domestic legal system, because of a lack of capacity or political will. This tool lays out some of the policy considerations that pertain to internationalizing the process, for instance through the creation of international or hybrid tribunals. It is not a comprehensive evaluation of all of these initiatives, as each merits a detailed study in its own right. Rather, its purpose is to gain practical insights from past experiences that may help in executing complex operations in often adverse circumstances. 1 S ee the Secretary-General’s report on the rule of law and transitional justice in conflict and post-conflict societies (S/2004/616, para. 34): “While the international community is obliged to act directly for the protection of human rights and human security where conflict has eroded or frustrated the domestic rule of law, in the long term, no ad hoc, temporary or external measures can ever replace a functioning national justice system.” 2 Ibid., para. 40. 3 Rome Statute of the International Criminal Court, art. 17. 4  ote that many of the issues raised may also be relevant to the investigative functions of international commissions of inN quiry.