Omri Sender and Michael Wood
The present contribution seeks to provide a general overview of the theory and practice concerning the question of how customary international law emerges. Raising some of the central issues rather than offering hard-and-fast answers, it suggests that although the process of formation of customary international law may defy exact definition in light of its inherently informal nature, important signposts exist for those who seek them. In particular, while scholars continue to debate how customary international law is generated, a shared understanding of the essential requirements does exist in practice among States and various international actors, who continue to regard customary international law as deriving from ‘a general practice accepted as law’. Such an understanding of how customary international law comes into existence and what it essentially is, is crucial for establishing a greater certainty with regard to its content and for the legitimacy of international law more broadly.