Antioxidants have attracted immense interest of researchers because of their implied role in the protection of biological systems. Though all living organisms possess their own antioxidant defense systems, no one can disregard the importance of dietary or exogenous antioxidants as these have an important role in the prevention of a variety of diseases. Several studies have revealed that polyphenols play an important role in free radical scavenging and therefore produce various biological and pharmacological actions. Some evidence suggests that the biological actions of polyphenols are related to their antioxidant activity because of the presence of galloyl moiety. The purpose of this book is to serve as a beginners guide to what reactive oxygen species and antioxidants are and to briefly review the role of polyphenols as an antioxidant. This book is also a special tribute to late Professor Pritam Dev Sharma who has extensively worked on free radicals, antioxidants and polyphenols.