Part I. Introduction.- Chapter 1. Methodological framework and research questions.- Chapter 2. Preliminary observations on the systems of enforcement.- Part II. The Characterisation and Prosecution of Core Crimes: Some Underlying Assumptions.- Chapter 3. Multi-level prosecutions of serious crimes of concern to the international community.- Chapter 4. Why do we need to understand the concept of core crimes?.- Chapter 5. What is required to intrude into the sovereignty of a defaulting State in order to investigate and prosecute core crimes?.- Chapter 6. The overarching contextual (juridical) elements.- Chapter 7. The juridical consequences of core crimes: Individual criminal responsibility and State aggravated responsibility.- Chapter 8. Detecting the determining and distinguishing factors.- Part III. The Vertical System of Enforcement.- Chapter 9. The salient features of the vertical system of enforcement.- Chapter 10. The State obligation to cooperate under international law.- Chapter 11. Inherent limitations of the vertical system of enforcement.- Chapter 12. The ensuing 'jurisdictional joint venture', a division of labour par excellence.- Part IV. The Horizontal System of Enforcement.- Chapter 13. Aut dedere aut judicare.- Chapter 14. The reliance of the horizontal system of enforcement on the corpus juris relating to extradition.- Chapter 15. The impact of customary international law and the general principles of law on the horizontal system of enforcement.- Chapter 16. Pitfalls within the horizontal system of enforcement.- Chapter 17. Concurrent State obligations.- Chapter 18. The self-assumption of jurisdiction: An abuse of power or a necessary evil?.- Part V. Conclusion.- Chapter 19. The obligation of States to prevent, prosecute and punish core crimes.- Chapter 20. The development of functional international constitutionalism.- Chapter 21.