The textbook provides a broad-brush overview of international law and its functioning. Its key legal institutions are explained as part of the international social and political process. They are compared with domestic legal systems, highlighting both differences and similarities, while emphasizing the crucial relevance of domestic implementation of international rules. In addition to the structural aspects of international law, the principal bodies of international substantive rules of conduct are illustrated, with special focus on the law governing the use of force, international criminal law and justice, investment and trade law, the law of the sea, human rights law, environmental law, jurisdictional immunities, and migration law. Throughout the text, international organizations, with particular attention to the UN, are presented as the forum for international dialogue, with international law serving as its language.