Genocide, crimes against humanity and war crimes are the most serious crimes of international concern. These international crimes, such as committed in the Former Yugoslavia, Rwanda or Cambodia and, earlier, during World War II and in Armenia, entail widespread mortality and victimisation, as well as long-lasting societal trauma and disruption, that may take generations to heal. While for some conflicts, domestic courts have eventually prosecuted these crimes, the international community has established international criminal courts and tribunals to ensure that ?justice is done? and the most culpable perpetrators do not go unpunished. However, the simultaneous operating of these different legal systems - with different legal traditions and differing dogmatic underpinnings - has generated incidents where perpetrators of similarly serious crimes received widely different sentences. It has, however, not been established how structural such inconsistency is. Inconsistency may be problematic not only from a normative point of view by violating the principle of equality and fairness, but may threaten the legitimacy of international criminal justice. Indeed, surveys have reported large discontent in post-conflict societies with international criminal justice and in particular with the leniency and ?unfairness? of sentences at the international level. This study has been designed to address this situation. By combining qualitative legal case file analysis with quantitative regression analysis, it will assess to what extent inconsistency of sentencing of international crimes occurs, as well as identify factors that generate inconsistency. The findings will be laid down in an ?International Sentencing Handbook? that will, employing domestic as well as international academic and legal practitioners expertise, offer remedies to harmonize the sentencing of international crimes. The study is not only innovative from an academic perspective, but is also vital for the acceptance by post-conflict societies of international criminal courts and tribunals, which will in many instances remain crucial to hold accountable the perpetrators of the most heinous crimes.