Written by one of the world’s leading international lawyers, this is the new and updated edition of Jan Klabbers’ landmark textbook. International law can be defined as ‘the rules governing the legal relationship between nations and states’, but in reality it is much more complex, with political, diplomatic and socio-economic factors shaping the law and its application. This refreshingly clear, concise textbook encourages students to view international law as a dynamic system of organising the world. Bringing international law back to its first principles, the book is organised around four questions: Where does it come from? To whom does it apply? How does it resolve conflict? And what does it say? Building on these questions with both academic rigour and clarity of expression, Professor Klabbers breathes life and energy into the subject. Footnotes point students to the wider academic debate while chapter introductions and final remarks reinforce learning. This third edition includes references to new case-law and literature, and features brief discussions on recent topics of general interest, including Brexit and the worldwide outbreak of the Coronavirus.