The book gives an account of international criminal law from the perspective of a formalist, positivist public international lawyer. It complements the usual consideration of the customary international crimes of genocide, crimes against humanity, war crimes, and aggression and of the workings of the various international criminal courts and tribunals, past and present, with a fuller-than-usual treatment of the customary international rules governing national jurisdiction to prescribe and to enforce criminal law; of the raft of universal multilateral treaties defining and creating obligations for states parties in respect of international crimes and of the so-far unsuccessful attempts to conclude a comprehensive universal criminal convention on international terrorism; of the prosecution and adjudication of international crimes at the national level, including by special domestic criminal courts; and of the legal bars, both international and domestic, to the prosecution and adjudication of international crimes at the national level. The book also features detailed conceptual analyses of the notions of an ‘international crime’ and an ‘international criminal court’, as well as an analytical account of the rise of individual criminal responsibility under international law.