It is widely recognised that international law is becoming increasingly fragmented into various fields governed by own principles and rules. Known as the phenomenon of fragmentation, such a functional specialization is generally regarded as a characteristic of modern international law. From international legal perspective, there are two main methodological approaches to fragmentation. The first one is represented by the Report on Fragmentation of the International Law Commission (ILC) of 2006.'It establishes a set of basic guidelines on normative conflicts and is entirely based on provisions of the Vienna Convention on the Law of Treaties (VCLT) of 1969.2 The second one is represented by the idea of constitutionalisation of international law. This is a theoretical approach and refers to the process of constitutionalisation of both the entire international legal system and functional regimes of international law.

Existent approaches to fragmentation aim at restoring coherence and unity within international law. Although there is no universally accepted definition of either fragmentation or international law, 3 proponents of the constitutionalisation of international law assume that fragmentation is a characteristic of modern international law. However, the main problem associated with the idea of constitutionalisation is that, in light of the uncertainty surrounding the phenomenon of fragmentation, the ultimate purpose of scholarly contributions on constitutionalisation becomes questionable. Such contributions fail to provide any terminological or theoretical justification for the use of constitutional language in international law. Equally they do not provide any definition of fragmentation, which is the problem they are trying to redress. An argument is therefore made that although the nature of contested concepts can be maintained in relation to any key concept in law in general, and international law in particular, conceptions of international constitutionalism turn out to be grounded on unstated assumptions.