Professor Conklin's analytical effort to explain the nature of jus cogens is not only highly impressive, but also very timely. It demonstrates the continuing relevance of jus cogens as it increasingly arises in multiple areas of international law, regardless of doctrinal calls from the 1980s onwards that it should have faded away. Since then, there have been those who have suggested that jus cogens does not make sense and should be abandoned, those who suggest that jus cogens has merely aspirational relevance and does not make a difference on the ground, and those who argue that jus cogens is merely "primary" law, not to be applied in the area of enforcement. What happens interestingly � and problematically � is that doctrinal debates on the conceptual rationale of jus cogens and on its more specific effects are often pursued separately. Conklin's contribution is a gentle reminder of the crucial issues of the background and essence of jus cogens that both writers and practitioners often tend to overlook hen addressing the implications of jus cogens in specific areas of international law.