Global risks present formidable challenges to international law. Although they have long been identified in many other scientific disciplines, they are currently only considered on a sectoral basis in international law in the absence of a legal definition. The aim of this book is threefold: to identify the main elements that characterise global risks in a legal perspective, to determine the characteristics that make them a new category of risk, and to analyse the changes they bring about in the main mechanisms of international law. Drawing on the relationship between international law and other legal systems, and in particular national law, this book highlights possible responses to the challenges posed by global risks. The study is based on extensive practice related to the examples of climate change and pandemics, but opens up perspectives on conclusions that could be common to other global risks, such as financial risks or cyber risks.