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.