Complexity and emergence are buzzwords in our modern world. But what do they mean? And how can they help us to see and to understand the world in a diff erent manner? Complexity and emergence are key concepts in the study of non-linear dynamic systems. Theories about these ‘complex systems’ attempt to explain how relationships between components of the system give rise to patterns of collective behaviour that defi ne the properties of the ‘whole system’, which interacts and forms relationships with its environment. A complex system contains many autonomous components which interact with each other-for example, human society and the economy, insect colonies, cellular automata on computers, some chemical systems, and other systems in various domains. Nature and society are two examples of dynamic, nonlinear systems. Both realms can be defi ned in terms of the individual elements they are composed of and by the relations between these elements. Many of these elements will themselves be complex systems; the large-scale systems are composed of a hierarchy of subsystems.