This dissertation explores the place that jus cogens occupies in contemporary international legal thought and practice. More specifically it looks at the place that the concept occupies within the discourse surrounding constitutionalism in international law. The question is asked whether it is viable to posit a specific constitutional structure for international law and whether such structure can be legitimized by the existence of certain values that are held in common by the international community. Both structural and value-based approaches posit a place for norms of jus cogens as possibly being seen as constitutional norms to some extent. Jus cogens as a now widely accepted concept in international law, continues to be the subject of much contemporary debate. The nature and function of the concept as proposed by various authors is looked at and the problematic aspects set out. Although there is a large amount of literature acknowledging the existence and importance of jus cogens, this has not been supported by international judicial practice. It seems that it is the practical difficulties surrounding the functioning of normative hierarchy that is the main reason for this. Chapter 1 introduces the approaches to the constitutionalism debate that have posited a legitimate place for norms of jus cogens. It also provides an introduction to the concept of jus cogens within contemporary international law. Chapter 2 starts out by defining certain concepts involved in the discourse surrounding constitutionalism. The strands of thought involved in the constitutionalism debate are then set out in order to provide the context for the placements of jus cogens posited by various authors. Chapter 3 looks at the evolution of the concept of jus cogens and the limited practical effect that has been given to the concept in international judicial practice. The main consideration here is the perceived inapplicability of jus cogens within cases concerning jurisdictional immunity. It therefore seems that jus cogens is, in general, limited to application against rules directly contradicting the substance of the jus cogens norm. Chapter 4 provides a critique of normative hierarchy theory, which is a main aspect dealt with in much constitutionalist thought. The chapter shows how the proposed functionality of normative hierarchy theory is unconvincing as only negative prohibitions can function as jus cogens under this construction. This further limits the instances where jus cogens can be seen as effective under constitutional thought. Chapter 5 concludes that under a strict conception of normative hierarchy, jus cogens is unlikely to receive much practical legal effect. This is due to the inapplicability of jus cogens in procedural matters and the limited number of norms that can function as jus cogens under normative hierarchy.