This book provides the first comprehensive introduction to the role of humanity in international law, offering a fresh perspective to a discussions with global implications. The 1990s and the first decade of the twenty-first century witnessed the sporadic emergence of a new vision of global law. Although the vision has taken many different forms, all instances of it have been uniform in the attempt of radically altering how we understand international law by seeking to posit the human as the primary subject of the international legal order and humanity as its main source of legitimacy. Together, this book calls these instances "the law of humanity project". In so doing, it also paints a picture of and critically assesses a particular moment in the history of international law - a moment which may have already come to a sudden end as a consequence of the current populist backlash in world politics, but during which it seemed inevitable that the law of humanity vision would come to play an increasingly important role in world affairs. This work harmonizes the different concepts encapsulated by the project and charts its 'rise, fall and potential rebirth'. The author importantly critiques how the language of humanity has been detrimental in achieving the changes in the international system that have been argued for by theorists on the law of humanity. Focusing on human rights, human security, and human dignity as core concepts in the law of humanity project, Soirila challenges the echo chamber in which many academics reside ? a useful synthesis of a broad range of theoretical approaches ? I hope that this work will help bring the broad church of humanity theorists together.