This book is the first comprehensive interpretation of the political and international thought of one of the greatest German political writers of the eighteenth-century, Johann Heinrich Gottlob von Justi (1717-1771). By revisiting his conceptions of natural law, happiness, the state, universal monarchy, the balance of power and international order the study reveals a much more original and diverse thinker than has previously been assumed. Building on ideas of a passionate human nature, Justi effected a passage from natural law to political economy that took into account the development of commercialism. The book firmly situates Justi in the German Enlightenment, and the German Enlightenment in a broader European context.