Mixing may be thought of as the operation by which a system evolves from one state of simplicity (initial segregation) to another state of simplicity (complete uniformity). Between these two extremes, complex patterns emerge and die. Questions naturally arise - how can the geometry of complex patterns be characterized? What is the time scale of the process? What structures are involved in the flow? This volume, comprising the proceedings of the NATO ASI on Mixing, attempts to address these questions from the approaches of geometry, kinetics and structure. The ASI which brought together diverse communities with a common interest in the problem of mixing, now provides us with a comprehensive work on the problem of mixing.