The chapter begins by discussing the history of the codification of the law of State responsibility. It then considers the current regulation of State responsibility, by distinguishing the ‘ordinary’ legal regime and the ‘aggravated’ State responsibility, and goes on to explore the main differences between the two regimes. It focuses on the elements of the internationally wrongful act, particularly on the attribution of conduct to a State and the relevance of fault and damage. In addition, it examines the circumstances which preclude wrongfulness and the consequences of the internationally wrongful act (with particular reference to the obligation to provide reparation).