This publication contains an extensive overview of free radicals and diseases, including both basic science approaches and clinical applications. The research of the last decades has contributed substantially to the understanding role and function of these metabolites. It is the aim of the editors to include a large variety of biological models ranging from yeast over mitochondria, isolated cells and cell culture models to animals and humans. The topics discussed focus on the function and integrity of mitochondria under oxidative conditions, the role of protein oxidation and proteolysis in the cellular stress response. Also the new aspects in the fields of antioxidant treatment are dealt with intensively. Some chapters are introducing more methodological approaches and their application in the investigation of oxidative stress and diseases related to this condition.