Every form of life in the world is connected: individuals, groups, businesses, governments. There is no such thing as total isolation. Many of these connections are plain to see, and it is a commonplace to say we live in a global village. Crucially, though, the various links and relationships have been difficult for classical analysis to understand and predict. As networks and connectivity are central to the human experience, there has been a long history of trying to understand these linkages and to predict their influences and impacts; but the traditional approaches have yielded unsatisfactory explanations. Many attempts at analysis have centred round ideas of describing the world in terms of free independent agents. But it is agents' 'linkages', both strong and weak, that underpin much of human activity. Whether it is stock market moves, sudden adoption of new technologies, or the unexpected consequences of long chains of events, the inter-connectivity of life appears to defy simple explanation. In this revealing work the authors draw on multiple sources to uncover the answers to the big questions about group behaviour, connections and the complex relationships that drive our world. In particular: - What happens when agents interact? - Is it possible to make sense of all these connections? - Why are some connections more important than others? - In a world of hugely complex and intricate links, what are 'super spreaders', and why are they critical? - Can we measure and model 'emergence'? - What are the new approaches and thinking we need to embrace and understand the world around us?