Mesoionic compounds are dipolar five or six membered heterocyclic compounds in which both the negative and the positive charge are delocalized, for which a totally covalent structure cannot be written, and which cannot be represented satisfactorily by any one polar structure. The most important member of the mesoionic category of compounds is the sydnone ring system. Sydnones are mesoionic compounds having the 1, 2, 3-oxadiazole skeleton bearing an oxygen atom attached to the 5 position. Sydnones are dipolar, pseudo-aromatic heterocycles with a unique variation in electron density around the ring. These characteristics have encouraged extensive study of the chemical, physical, and biological properties of sydnones, as well as their potential applications. A large number of sydnone derivatives have been synthesized with biological interest and reported to possess a wide spectrum of biological and pharmacological activities like antimicrobial, anti-inflammatory, analgesic, anti-pyretic, antitumour, antiarthritic and antioxidant properties. The research and development of new sydnone functionalisation methods in conjunction with the cycloaddition reactions will provide the focus of future research in the development of sydnone drugs. Thus there is wide scope for structurally modified sydnone derivatives to explore more potent biodynamic molecules.