State responsibility is that oddest of international legal institutions, theoretically omnipresent but rarely visible as practical implementation. There is a sense in which the institution appears simply tautologous with the totality of international law itself. Isn’t every legal subject “responsible” for carrying out their obligations? Isn’t it part of the very definition of a legal rule – in contrast to other rules – that it is accompanied by the “responsibility” of the one who breaches them? The word plays tricks on its users: it designates both the rule (“you have a responsibility to do this”) and the consequences of the rule (“breach of obligation entails responsibility”). In such ways, responsibility penetrates all legal thinking and practice, underlining the seriousness of the legal system and the duty of the subjects of that system to comply. And yet it is seldom applied as such. States may readily agree to ex gratia payments to settle disputes with their neighbours – but responsibility is seldom recognized, perhaps to avoid the tone of moral condemnation it may engage.