This textbook provides an overview of the functioning international law, rather than the full knowledge of the immense developments of international law of the last decades, concerning the regulation of its subjects, sources, state responsibility, the means of dispute settlement and the ever increasingly problematic relation to domestic jurisdictions and the numerous branches of substantive international law, such as the law of the sea, environmental law, human rights law, investment and trade law, international criminal law, and jurisdictional immunities, amongst others. The extreme concision book is aimed to provide an incentive for the students at first degree level to study the subject, while purporting to complement the specific syllabus, which may be chosen by the teacher of the PIL module. The basic character of the narrative is also meant to embolden domestic attorneys to realise how intertwined with international law are the rules and institutions they interpret and apply on a daily basis, and how many more arguments they could plead before a domestic court if they were aware of this.