This book deals with the basic knowledge of crisp, rough, fuzzy and intuitionistic fuzzy sets. The book gives a clear picture of definition and the properties it satisfies along with the few properties it denies. While writing this book, our aim was to reach the basic concept of Intuitionistic Fuzzy Sets and its extensions. Numerous operators defined in Intuitionistic Fuzzy Set gives a clear picture of the transformation of an Intuitionistic Fuzzy Set into its basic Fuzzy Set.