The Principles of Heterocyclic Chemistry presents a unified account of fundamental heterocyclic chemistry with the emphasis placed on the correlations between the methods of preparation and the properties of the various ring systems. This book opens with an introductory chapter that discusses fundamental concepts of the electronic theory of organic chemistry and the relationship of heterocyclic and carbocyclic aromatic compounds. This is followed by separate chapters on the chemistry of the six-membered ring compounds containing one or more heteroatoms, five-membered ring compounds, three- and four-membered rings, and the physical properties of representative heterocyclic compounds. Each chapter begins with introductory section that surveys the various ring types, gives the systems of nomenclature and numbering, and mentions a few important natural and synthetic compounds. Syntheses starting from aliphatic and carbocyclic compounds are then given. The preparation of one heterocyclic compound from another is considered as a reaction of the starting material. The reactions of aromatic and non-aromatic compounds are discussed separately. This book contains the essential heterocyclic chemistry required by an Undergraduate or Graduate student for his course-work, and it is hoped that it will be found stimulating by many a more senior teacher and researcher.