This textbook has been prepared to cover, in full detail, the course “Heterocyclic Compounds and Stereo Chemistry (Theory)” of the B.Pharm curriculum. It brings together the chemistry of carboxylic acids, phenols, amines and polynuclear aromatic hydrocarbons; the principles of optical and geometrical isomerism; and the systematic chemistry of five-membered and other important heterocyclic ring systems that form the backbone of a very large number of drug molecules in use today. Each unit follows the prescribed syllabus topic-by-topic and includes: definitions and classification, methods of preparation, mechanisms of important reactions, structure–activity relevance, named-reaction schemes with reagents and conditions, and the pharmaceutical/medicinal significance of the compounds discussed. Wherever chemically meaningful, structures and reaction schemes have been drawn to help visualise the transformation rather than simply stating it in words. This book is intended as a study companion for undergraduate pharmacy students and is best used alongside a laboratory manual and standard reference texts such as Finar’s Organic Chemistry and March’s Advanced Organic Chemistry, which are cited throughout for further reading. — Dr. C. Sankar, Professor