The case concerning the factory of Chorzów (1927–1928) is known as a landmark in public international law: its reasons are often quoted with regard to issues of competence of international courts and of state liability. This contribution proposes to contextualize the case in line with the Versailles Treaty, the question of reparation, the special situation of Upper Silesia and the recognition of Germany’s rights against Poland’s claims. In order to settle this case, the judges of the Permanent Court of International Justice had to disentangle a complex configuration in which public and private interests were intimately mixed. In doing so, they discussed arguments that were based on rules of private law concerning ownership, contracts and torts. Without quoting any national law, the Permanent Court of International Justice transplanted a kind of common private law (inspired by some recent developments in European countries of the time) into “general principles” of international law.