The book discusses chemistry (methods of synthesis, reactions and importance) of three-membered heterocyclic compounds (containing one or two heteroatoms), four-membered heterocyclic compounds, five membered heterocyclic compounds (containing one or two or more than two hetero atoms) alongwith their benzofused derivatives and six-membered heterocyclic compounds (containing one or more than O, N or S heteroatoms) alongwith their benzofused derivatives. The incorporation of pyridazine, pyrimidine and their derivatives alongwith their fused derivatives has special importance. Seven-membered heterocyclic compounds and meso-ionic heterocycles have also been included.