This book is written for B.Sc., B.Sc. (Hons.) and M.Sc., students. The subject is presented in a very systematic manner. Simple language is used, diagrams/illustrations are generously used to emphasise reaction. Sites, to indicate reaction pathways. Emphasis is placed on the correlation of the structure of functional group with its properties. A detailed molecular orbital and valance bond interpretation of the structure of each functional group is given. This enable the student to predict the properties of the functional group. Fundamental principles of energetics, reaction rates and stereochemistry are provided to lay a strong foundation. Mechanisms are described in a step by step manner.