If a butterfly flaps its wings in Brazil, does it cause a tornado in Texas? Choas, the most important advance in science since the advent of Quantum Theory, attempts to answer such baffling questions. The discovery of randomness in apparently predictable physical systems has evolved into a new science that declares the universe to be far more unpredictable than we have ever imagined. This book explains how chaos makes its presence felt in many varieties of event, from the fluctuation of animal populations to the ups and downs of the stock market. It also examines the roots of chaos in modern mathematics and physics, and explores the relationship between chaos and complexity, the new unifying theory which suggests that all complex systems evolve from a few simple rules. This is an accessible introduction to an astonishing and controversial theory that could dramatically change our view of the natural world and our place in a turbulent universe.