Chaos, that is irregular dynamical behaviour, is ubiquituous in nature and occurs in a wide range of systems including lasers, fluids, etc., heart beats and brain waves. Before 1990 the emergence of chaos in a system was mostly considered as a nuisance because chaotic systems are hard to predict due to their sensitivity to small perturbations. After 1990 it became clear that this sensitive dependence offers the unique possibility to control these systems with a minimum of additional energy.This handbook provides a comprehensive up-to-date overview of the field. It starts with an introduction to chaos theory, and covers all known methods of chaos control from parametric feedback to neuronal networks. A large part of the handbook is devoted to applications which range from control of electronic circuits, the control of lasers and chemical plants up to "antichaos control" in biological systems which offers the possibility to avoid epileptic seizures.