The starting point for discussion and analysis of the sources of international law is almost invariably art 38 of the Statute of the International Court of Justice (‘ICJ Statute’), the International Court of Justice being the primary judicial organ of the United Nations. Article 38 lists the sources of international law as comprising treaties, custom, general principles of law, and – as subsidiary means for determining the law – judicial decisions and academic writing. However, in the 75 years since the adoption of the ICJ Statute, newer sources of legal obligation have emerged for the international community. These often involve non-state and intergovernmental actors in their creation. This chapter explores both the traditional and newer sources of international law and assesses how they are adopted and created.

Although the Vienna Convention on the Law of Treaties devotes nine articles to invalidity of treaties, cases rarely arise in practice. Circumstances covered by the Convention include violation of internal law, error, fraud, corruption, coercion and violation of a peremptory norm of international law (jus cogens). Article 46 of the Convention covers the first of these, providing that a state may not invoke the fact that its consent to be bound has been expressed in violation of its internal law unless that violation was manifest and concerned a rule of fundamental importance. The chapter examines the meaning of the key terms of this provision and possible cases in which this might arise. In the context of coercion, the chapter looks at treaties which might be concluded by the threat or use of force, peace treaties and unequal treaties. The scope of peremptory norms (jus cogens) is also discussed, together with the consequences of invalidity.

The chapter deals with the role of the ICJ in the development of international law from both a doctrinal and a practical perspective. It considers concrete examples of the way in which the Court’s judgments and opinions have had an influence on the development of international law, and it concludes that the Court has in practice had a significant impact on the development of international law, even though that goes beyond its core mandate.

The chapter traces the origins of human dignity, showing how it was originally used to denote titles of honor but is now seen as a universal human right or as undergirding universal human rights. In the context of discussing dignity rights, the chapter highlights international human rights treaties and national constitutions making refeerence to the concept of human dignity, which, in modern usage, has to do with the inherent worth of a life. The chapter discusses how human dignity is the foundation for many human rights, including the right to life, the right to be free from torture and other forms of cruelty, and the right to be free of discrimination. The chapter describes existing jus cogens norms prohibiting various acts that violate fundamental human rights, concluding that the death penalty must be abolished because it makes use of credible death threats, inflicts psychological torture, and violates an array of basic human rights. The chapter details how non-lethal corporal punmishments have already been abandoned and how the death penalty has been abolished or curtailed in many countries, with international criminal law tribunals precluding the death penalty's use.

The Introduction gives a snapshot of the current status of capital punishment around the globe. It gives current statistics from Amnesty International and describes Amnesty International's anti-death penalty campaign in the 1970s that led to the Declaration of Stockholm, which expressed "total and unconditional opposition to the death penalty." The Introduction describes the divide between retentionist and abolitionist countries, highlighting countries that have outlawed capital punishment in their constitutions or through judicial rulings. After detailing how the death penalty was traditionally seen as something other than torture, the Introduction discusses the law's evolving nature--and how the death penalty is increasingly seen as a torturous and cruel punishment that violates human dignity and fundamental human rights. Noting that death sentences are no longer treated as a "lawful sanction" in many locales, the Introduction describes how the U.N. General Assembly has voted on multiple occasions for a global moratorium on executions. The Introduction summarizes the current state of international law as regards capital punishment and previews the book's content.

As a doctrine of positive international law, jus cogens superveniens gives juridical effect to the natural law’s prohibition of conduct violative of aspects of the transnational common good that reflect absolute human rights. In order to be fully valid in the sense that it commands a moral obligation of compliance, a measure for regulating the life of a community must be reasonable. A measure cannot be reasonable if its purpose is not the preservation or enhancement of the common good. The common good is the full array of physical, cultural, and institutional arrangements that facilitate the ability of persons in their various communities, including the transnational community, to advance their human flourishing. Human rights are conclusions of practical reason that always constitute essential aspects of the common good. Some human rights are ‘absolute’ in that they are not subject to limitation or restriction on any grounds, because any such limitation or restriction can do nothing but damage the common good. Although natural law is binding in reason, the positive law and other juridical measures of official authority are frequently required to effectively serve the common good.

This chapter discusses how customary international law enters the sphere of EU law and to what extent it determines the relationship between the EU institutions, its member states and individual persons. Against this background, it is examined how customary international law is integrated into the EU legal order, what status it enjoys within that legal order, how it can be applied by EU institutions and whether it can serve as a benchmark for judicial review. Assuming that EU law is an autonomous domestic legal system, these questions are discussed from the perspective of EU constitutional law. Here it is argued that the Court of Justice of the European Union, in evaluating these issues, focusses too much on the idea of the autonomy of EU law. In order to provide provisions of customary international law with practical effect the validity of EU law must also be able to be reviewed on the basis of international law standards.

After the discussion of the powers of the Security Council in the previous chapter, this chapter considers some of the limitations on these powers, real or imagined. In particular, it examines limits deriving from the Purposes and Principles of the United Nations and the norms of jus cogens. Then, it explores some checks and balances on the actions of the Council. Ultimately, our response is that states do not have the right to do this, and would be acting unlawfully if they purported to exercise such a right. But they do, of course, have the ultimate option as a matter of policy of simply disregarding binding obligations imposed by the Council, with all the consequences, political and legal, that might flow from such a course of action. That is why the Council needs to exercise self-restraint and use its undoubted powers responsibly and only where it really is necessary to do so in order to ensure prompt and effective action to maintain international peace and security. This is the most effective check on the Council’s power.

The first chapter of the book outlines the status of the right to life under international law. It concludes that the right to life is both a customary rule and a general principle of law while the prohibition on arbitrary deprivation of life is a peremptory norm of international law (jus cogens).

The chapter considers the jurisdictional aspects of the right to life looking at the geographical, material, personal, and temporal aspects. The universal application of the jus cogens content of the right to life is affirmed alongside consideration of jurisdictional issues under regional human rights treaties.

This chapter summarises the customary rules pertaining to the right to life. They bind not only States but also international organisations and, with respect to specific rules in certain circumstances, also non-State actors. The chapter further identifies those rules of general international law that have attained the status of peremptory norms (jus cogens) on the basis of their acceptance and recognition as such by the international community of States as a whole. Such norms bind all actors, whether State or non-State in character. Finally, the chapter delineates those rules that are custom in the making – de lege ferenda – but which have not yet crystallised, for want of opinio juris that is both general among States and specific among those States that are specially affected by it.

The prohibition of slavery is not only a customary rule of international law, it is also an international crime and a norm of jus cogens. Slavery has been famously described as ‘social death’, but this chapter considers whether, and in which circumstances, it may also constitute a violation of the right to life.