A heterocyclic compound possesses a cyclic structure with two or more different kinds of atoms in the ring. In this Monograph, learners will be able to know about the most important simple heterocyclic ring systems containing heteroatom and their systemic nomenclature and numbering. They can understand and discuss the reactivity and stability of hetero aromatic compounds. Study the important synthetic routes and reactivity for five and six-member heteroaromatic compounds. Understand the important physical and chemical properties of five and six-member heteroaromatic compounds. Know about the applications of these heteroaromatic compounds in the industrial and pharmaceutical companies.