Book describes an overview on Heterocyclic compounds. Among the heterocycles fused-heterocycles represent a dynamic class of organic compounds with notable medicinal and agrochemical properties. These privileged structure exhibit broad spectrum of pharmacological and biological activities including antiviral antifungal anticancer antimycobacterial antiulcer antitumor anti-HIV antianxiety antihistamine anti-inflammatory analgesic antileishmanial genotoxic anticonvulsant hyponotics anthelmintic herbicidal insecticidal anticorrosive antioxidant dyestuff and flavoring agents.