This chapter begins with the history of the international recognition of terrorism as a crime, including through the adoption of global and regional counter-terrorism treaties, and United Nations (UN) Security Council resolutions. The chapter then turns to a discussion of the challenges associated with defining terrorism, including its material and mental elements, and with national prosecutions. The chapter also explores terrorism as a war crime, a crime against humanity, and a crime under customary international law. The chapter’s consideration of torture begins with the definition found in the UN Convention Against Torture, and considers the obligation to prosecute or extradite (aut dedere aut judicare) under that treaty. It also discusses torture as an international crime under the ICC Statute and other statutes of international criminal tribunals. The chapter ends with an examination of ecocide as an emerging crime.

Chapter 5 examines the individual conduct elements of the crime of aggression, namely ‘the planning, preparation, initiation or execution, by a person in a position effectively to exercise control over or to direct the political or military action of a State’. It considers the extent to which this language makes the crime of aggression a ‘leadership’ crime.Also examined is the individual contribution that must be made by an accused in order to reach a conclusion that an individual has ‘committed’ a crime of aggression, in particular the meaning of the terms ‘planning’, ‘preparation’, ‘initiation’, and ‘execution’, as well as the relevant mental elements. The interaction of the leadership requirement with Rome Statute provisions relating to superior orders and the responsibility of commanders and other superiors is discussed, as is the relevance of the defences of mistake of fact and mistake of law. Finally, the chapter considers the different modes of liability that attract individual criminal responsibility under Article 25(3) of the Rome Statute and whether it is theoretically possible for a leader to order, aid, abet, or attempt a crime of aggression.