This chapter looks to make sense of the paradox of change in the United Nations system, whereby an alteration in the behaviours of the Member States can modify the rules of the Organization that bind the same Members: rule-breaking behaviour becomes rule-making behaviour. By looking to complexity theory, which is fundamentally a theory of change, it shows how we can think of the UN ‘system’ as the emergent property of the actions and interactions of the Member States, evolving as they respond to new information about events in the outside world or the unexpected actions of another State.