Customary international law is one of the principal sources of public international law. Although its existence is uncontroversial, until now the content of customary international law in the area of human rights has not been analyzed in a comprehensive manner. This book, from one of international law's foremost scholars and practitioners, provides an unparalleled account of the customary international law of human rights. It discusses the emergence of this customary law, the debates about how it is to be identified, and the efforts at formulation of customary norms. In doing so, the book provides a useful and accessible introduction to the content of international human rights. The author uses the Universal Declaration of Human Rights as a basis to examine human rights norms, and determine whether they may be described as customary. He makes use of relatively new sources of evidence of the two elements for the identification of custom: State practice and opinio juris. In particular, the book draws on the increasingly universal ratification of major human rights treaties and the materials generated by the Universal Periodic Review mechanism of the Human Rights Council. The book concludes that a large number of human rights norms may indeed be described as customary in nature, and that courts should make greater use of custom as a source of international law.