Argues that the foundations of many social science theories, especially those in political science, are faulty. Taking insights from complexity theory as a point of departure, this text observes that we live in a world where things are interconnected, where unintended consequences of our actions are unavoidable and unpredictable, and where the total effect of behaviour is not equal to the sum of individual actions. It draws on a range of human endeavours to illustrate the effect of these system effects. The book concludes by examining what it means to act in a system. It shows how political actors might modify their behaviour in anticipation of system effects, and it explores how systemic theories of political behaviour might account for the role of anticipation and strategy in political action.