Hans Nohl, Andrey Kozlov, Lars Gille, and Katrin Staniek: Endogenous oxidant-generating systems -- Peter Schroeder and Jean Krutmann: Environmental oxidative stress -- Helen Griffith: Chemical modifications of Biomolecules by oxidants -- Kelvin J.A. Davies: Broad spectrum of cellular reactions to oxidative stress -- Tilman Grune, Peter Schroeder, and Hans K. Biesalski: Low-molecular weight antioxidants -- Juan Sastre, Federico Pallardo, and Jose Vina: The glutathione system -- Grzegorz Bartosz: Superoxide dismutases and catalase -- Bente Riis, Henrik Poulsen: DNA-repair mechanisms -- Diana Poppek and Tilman Grune: Protein repair and degradation -- L.-O. Klotz: Metabolic regulation and gene expression in response to oxidative stress -- Enrique Cadenas and Alberto Boveris: Mitochondrial free radical production, antioxidant defenses and cell signaling. Oxidative stress is one of the major symptoms accompanying physiological functions and numerous diseases. Oxidants and free radicals are connected with diseases such as cancer, diabetes, infectious, cardiovascular and neurodegenerative diseases and also in the aging process itself. Therefore, comprehensive knowledge of the underlying mechanisms of oxidant and free radical production and the defence against this permanent threat to cells is important for the understanding of many physiological and pathophysiological processes. This book overviews the basic mechanisms of oxidant formation and antioxidant defences. In addition, the formation of oxidants and their detoxification, the damage of macromolecules and the major repair and removal systems will be highlighted.