Living organisms require oxygen for survival, but it is also a highly reactive molecule that can damage organisms by producing reactive oxygen species. Oxidation is the chemical reaction that produces free radicals and thereby leads to chain reactions with the potential to damage the cells of organisms. Antioxidants inhibit oxidation. Ascorbic acid or thiols are antioxidants that can terminate these chain reactions. Organisms have a complex system of antioxidant metabolites and enzymes that work in tandem to prevent oxidative damage to DNA, proteins and lipids. However, reactive oxygen species have useful cellular functions as well, such as redox signaling. Antioxidant systems therefore do not remove oxidants completely but keep them at an optimum level. The role of oxidative stress in degenerative diseases, such as diabetes, kidney disease, neurological disorders, obesity, cancer and aging is understood. This makes antioxidant dietary supplements a potential strategy to overcome these conditions. This book provides comprehensive insights into antioxidants and their role in human health and disease. It will also provide interesting topics for research, which interested readers can take up. With state-of-the-art inputs by acclaimed experts of this field, this book targets students and professionals.