As Chaos explained the science of disorder, Nexus reveals the new science of connection and the odd logic of six degrees of separation. How can geometry explain the puzzles of human behavior? In this incisive, insightful work Mark Buchanan presents the fundamental principles of the emerging field of small worlds theorythe idea that a hidden pattern is the key to how networks interact and exchange information, whether that network is the information highway or the firing of neurons in the brain. Mathematicians, physicists, computer scientists, and social scientists are working to decipher this complex organizational system, for it may yield a blueprint of dynamic interactions within our physical as well as social worlds. Highlighting groundbreaking research behind network theory, Buchanan documents mounting support for the small-worlds idea and demonstrates its multiple applications to diverse problemswhether explaining the volatile global economy or the Human Genome Project, the spread of infectious disease or ecological damage. Nexus is an exciting introduction to the hidden geometry that weaves our lives so inextricably together. 20 illustrations.