Free radicals are continuously produced in cells as a part of normal cellular function. However, excess generation of free radicals plays a critical role in the pathophysiology of many disease conditions, especially cancer, atherosclerosis, Alzheimer's disease, etc. Oxidation is a major chemical process that produces free radicals and initiates chain reactions that cause cellular damage. Compounds that inhibit oxidation are called antioxidants; phenols are known to possess excellent antioxidant properties. Phenolic compounds are abundant in plants in a wide variety of chemical structures. Natural phenolic compounds include phenolic acids and ester derivatives, flavonoids and benzopyran derivatives, quinones, tannins, lignins, lignans, stilbenes, essential oils, chalcones, etc. Nutraceuticals, in the name of dietary supplements and functional foods, are being consumed as prophylactics for the prevention of many diseases throughout the world. Most of these products are polyphenols; hence, this book provides an insight on therapeutic potentials of natural and synthetic polyphenols, emphasizing their pharmacology.