Human defensins are small antimicrobial and cytotoxic peptides produced by neutrophils and epithelial cells. They exhibit broad range of antimicrobial properties and are thought to be ideal therapeutic agents because of their potential ability to circumvent the problems of acquired resistance often observed with other antimicrobial therapies. Therefore studies have been started to clone and express these peptides in bacterial and plant systems. There are certain major hurdles of producing the defensins peptides in bacteria like toxic action of the peptide on the host cells, costs of production by these technologies and scale up is also very difficult. Transgenic plants as bioreactors pave a new way of producing recombinant therapeutic defensins peptides. The present review paper describes an overview of human defensins including its classification, molecular structure, biosynthesis, localization, mechanism of action, potential medical application and production of human defensins by r-DNA technology in bacterial and plant systems.